SD can refer to different things depending on the context. Here are some possible meanings:

• Standard Definition Television: This is a television system that uses a resolution that is not considered to be either high or enhanced definition. SDTV offers a similar resolution to the analog broadcast systems used when it was introduced. The two SDTV signal types are 576i (with 576 interlaced lines of resolution, derived from the European-developed PAL and SECAM systems), and 480i (with 480 interlaced lines of resolution, based on the American NTSC system). SDTV refresh rates are 25, 29.97 and 30 frames per second, again based on the analog systems mentioned. SDTV originated from the need for a standard to digitize analog TV and is now used for digital TV broadcasts and home appliances such as game consoles and DVD disc players.

• Standard Definition Video: This refers to any video that is not UHD or HD. SD videos are low quality, with lower bit rates and smaller file sizes. However, they are a good option for viewers on very slow internet connection speeds because the lower bit rate means they will stream more smoothly with less chance of buffering compared to higher quality videos. A broadly accepted cut-off point for SD video is 480p, meaning any video with 480 vertical pixels or less is standard definition.

• Secure Digital: This is a proprietary, non-volatile, flash memory card format developed for use in portable devices. SD cards are small and portable, making them ideal for use in smaller, thinner, and more portable electronic devices. The SD cards small footprint is an ideal storage medium for smaller, thinner, and more portable electronic devices. SD cards come in different capacities, with the SDHC format supporting cards with capacities up to 32 GB.

In summary, SD can refer to different things depending on the context, such as Standard Definition Television, Standard Definition Video, or Secure Digital.