Abbreviation for binary digit. Used in all digital communications. A bit is a binary unit, represented by either a "0" or a "1".
In many cases where "bit" is a measurement, more bits are better. This is because it refers to how many digits are in a binary (base-2) number. Each extra bit doubles the number of possible values.
For example, 10-bit color (commonly known as HDR) allows for 1,073,741,824 distinct colors, while 8-bit color can describe only 16,777,216 colors. (Color values are expressed in each of the red, green, and blue primary colors, so a "10-bit" color value is actually 30 bits.)
Similarly, 512-bit encryption uses a security key with many, many more possible values — and therefore better security — compared to 256-bit encryption.