Basically, MD5 (technically called MD5 Message-Digest Algorithm) is a cryptographic hash function whose main purpose is to verify that a file has been unaltered.
Giving any text string, the output will be an encrypted text string that can not be decrypted (theorically, yes).
MD5 Pros and Cons
MD5 was invented by Ronald Rivest, the first hash function he developed was MD2 in 1989, which was built for 8-bit computers.
MD2 was then replaced by MD4 in 1990. MD4 was made for 32-bit machines and was a lot faster than MD2.
MD5 was released in 1992 and was also built for 32-bit machines. MD5 isn’t as fast as MD4, but it is considered to be more secure than the previous MDx implementations.
Other cryptographic hash functions, like SHA-1, have been suggested as an alternative, since MD5 has also been shown to have security flaws.