MD5 is a widely used cryptographic hash function producing a 128-bit (16-byte) hash value, typically expressed in text format as a 32 digit hexadecimal number - Wikipedia.
This system is commonly used to check the integrity of files (like downloads). The way MD5 hashes are created, any slight variation in a file creates a new hash that is completely different than the previous, making changes in files (e.g. corruption in download or tampering) very apparent.
MD5 hashes are very standard, as they are always 128 bits, or 32-character strings.