SD
Abbreviation with 11 meanings
| Stands for | Standard deviation |
|---|---|
| Meanings | 11 |
| Categories | Units & Measurements, Geography & Places, Technology & Computing, Medical, Texting & Internet Slang, Sports |
SD has 11 meanings. The most common are Standard deviation (statistics) and South Dakota (US state); it can also stand for Secure Digital, Seborrheic dermatitis, Standard definition, Stable disease and San Diego, plus 4 more listed below.
Meanings of SD at a glance
| # | SD stands for | Context |
|---|---|---|
| 1 | Standard deviation | Units & Measurements › Statistics |
| 2 | South Dakota | Geography & Places › US State |
| 3 | Secure Digital | Technology & Computing › Computer Hardware |
| 4 | Seborrheic dermatitis | Medical › Dermatology |
| 5 | Standard definition | Technology & Computing › Consumer Electronics |
| 6 | Stable disease | Medical › Hematology and Oncology |
| 7 | San Diego | Geography & Places › City and Neighborhood |
| 8 | Sudan | Geography & Places › Country Code |
| 9 | Stable Diffusion | Technology & Computing › Artificial Intelligence |
| 10 | Sweet dreams | Texting & Internet Slang › Dating and Relationship |
| 11 | Split decision | Sports › Other Sports |
1. Standard deviation
Units & Measurements · Statistics Abbreviations · also used in medicine
A measure of how spread out values are around their mean, equal to the square root of the variance and expressed in the same units as the data. In a normal distribution about 68 percent of values lie within 1 SD of the mean and 95 percent within 2 SD.
Example: Participants were 34.2 years old on average (SD = 8.7).
The sample SD divides by n − 1 (Bessel's correction) rather than n to correct the bias in the sample variance. APA style reports it as M = 34.2, SD = 8.7, with the symbols in italics; Greek σ denotes the population SD and s the sample SD. Karl Pearson coined the term in the 1890s. SD describes spread in the data, whereas SE describes uncertainty in an estimate.
2. South Dakota
Geography & Places · US State Abbreviations
Admitted on November 2, 1889, alongside North Dakota and listed as the 40th state. Home to Mount Rushmore, the Black Hills and Badlands National Park; Pierre is one of the least populous state capitals, and Sioux Falls is the largest city.
Example: Mount Rushmore postcards are postmarked in Keystone, SD.
AP uses S.D.; the Government Publishing Office and older works use S. Dak. SD was assigned in 1963. SD also means Secure Digital memory cards and standard definition video, and it is Sudan's ISO country code. Pierre is pronounced like pier, not like the French name.
3. Secure Digital
Technology & Computing · Computer Hardware Abbreviations
Memory-card standard used in cameras, drones, laptops, game consoles and audio recorders, with full-size cards measuring 32 by 24 mm. Capacity tiers include SD, SDHC, SDXC and SDUC.
Example: Format the SD card in the camera before the shoot, not on your computer.
SanDisk, Panasonic and Toshiba developed SD in 1999, and the SD Association has managed it since 2000. "Secure" referred to built-in copy-protection features demanded by the music industry. Speed markings include Class 10, UHS U1 and U3, and video classes V30 to V90 for guaranteed sustained writing. A small sliding switch on full-size cards locks them against writing. In television, SD means standard definition.
4. Seborrheic dermatitis
Medical · Dermatology Abbreviations
Common chronic rash with redness and greasy yellow scale on oily areas such as the scalp, eyebrows, sides of the nose, ears and chest. Dandruff is its mildest form, and in infants it appears as cradle cap; the Malassezia yeast plays a role.
Example: SD of scalp and nasolabial folds; ketoconazole 2 percent shampoo twice weekly and hydrocortisone to face.
It is especially common and severe in people with HIV and Parkinson's disease. Treatments include antifungal shampoos and creams, mild topical steroids, calcineurin inhibitors and roflumilast foam, approved for it in 2023. In statistics SD means standard deviation, which appears far more often in medical literature.
5. Standard definition
Technology & Computing · Consumer Electronics Abbreviations
Video resolution of the pre-HD era: 480 lines in NTSC regions such as North America and Japan (typically 720 by 480 pixels) and 576 lines in PAL regions such as Europe. DVDs and analog TV broadcasts are standard definition.
Example: The old episodes only exist in SD, so they look soft on a 4K TV.
Standard-definition broadcasts were usually interlaced (480i or 576i) and traditionally 4:3, though widescreen SD also existed. Streaming services still offer SD tiers for slow connections. Upscaling SD to 4K requires TVs to invent most of the picture detail. In storage, SD refers to Secure Digital memory cards.
6. Stable disease
Medical · Hematology and Oncology Abbreviations
Tumor response category in which cancer has neither shrunk enough to qualify as a partial response nor grown enough to meet the threshold for progression, under criteria such as RECIST. It is often a meaningful outcome for slowly growing tumors.
Example: Third restaging scan shows SD; tolerating therapy well, continue for 3 more cycles.
Disease control rate (DCR) adds stable disease to complete and partial responses. Durable stable disease, for example lasting six months or more, can reflect real drug benefit with targeted therapies and in indolent cancers. In dermatology SD means seborrheic dermatitis.
7. San Diego
Geography & Places · City and Neighborhood Abbreviations
California's second-largest city, near the Mexican border, with a major US Navy presence and the annual Comic-Con convention. SD is common shorthand among locals and in sports.
Example: SD weather barely changes, which is why everyone moves here.
SD also means South Dakota, Sudan and Secure Digital cards. The airport code is SAN. San Diego was the first European settlement in California, founded by Spanish missionaries in 1769.
8. Sudan
Geography & Places · Country Code Abbreviations
Sudan, with Khartoum as its capital and SDN as its alpha-3 code, has more ancient pyramids than Egypt, built by the Nubian kingdoms of Kush. War from April 2023 drove the government to Port Sudan until it returned to Khartoum in January 2026.
Example: UN appeals for SD warn of one of the world's largest displacement crises.
South Sudan (SS) split from Sudan in 2011. In US addresses SD means South Dakota, and SD also means Secure Digital memory cards.
9. Stable Diffusion
Technology & Computing · Artificial Intelligence Abbreviations
An open-weight text-to-image model that generates and edits pictures from written prompts using a latent diffusion process. Because its weights can be downloaded, it runs on consumer graphics cards and supports a large ecosystem of community fine-tunes.
Example: The concept art was sketched in SD, then repainted by hand for the final cover.
Released in August 2022 by Stability AI with researchers from the CompVis group at LMU Munich and Runway, building on their latent diffusion research. Versions include SD 1.5, SDXL and SD 3. It has been at the center of lawsuits by artists and by Getty Images over training data. In hardware, SD means Secure Digital memory cards.
10. Sweet dreams
Texting & Internet Slang · Dating and Relationship Abbreviations
Bedtime wish, usually paired with GN (good night) as "gn sd," sent between partners, parents and children, or close friends.
Example: Gn and sd, love you, see you at breakfast.
Common in texts but easily confused with other senses: SD is the postal code for South Dakota, a nickname for San Diego and the name of the SD memory card format. The bedtime context makes the meaning obvious.
11. Split decision
Sports · Other Sports Abbreviations
Fight result in which two judges score the bout for one fighter and the third judge scores it for the other. Split decisions often prompt controversy.
Example: He took a SD despite being knocked down in the fifth round.
A split draw occurs when one judge favors each fighter and the third scores it even. In geography SD is the postal code for South Dakota, and in technology it refers to memory cards.
Related abbreviations
More statistics abbreviations
- RR – Relative risk
- RSS – Residual sum of squares
- RV – Random variable
- R² – Coefficient of determination
- SE – Standard error
- SEM – Standard error of the mean
- SPC – Statistical process control
- SRS – Simple random sample
See all 88 statistics abbreviations →
More US state abbreviations
- OR – Oregon
- PA – Pennsylvania
- RI – Rhode Island
- SC – South Carolina
- TN – Tennessee
- TX – Texas
- UT – Utah
- VA – Virginia
See all 51 US state abbreviations →
This entry is for general education and is not medical advice. Abbreviation use varies between institutions; always confirm in context.