In cryptography, MD5 (Message-Digest algorithm 5) is a widely-used cryptographic hash function with a 128-bit hash value. MD5 was designed by Ronald Rivest in 1991 to replace an earlier hash function, MD4. As an Internet standard, MD5 has been employed in a wide variety of applications including most of your online applications where sensitive information like passwords, credit card numbers, etc. are hashed and stored.
First of all, MD5 is not an encryption, but a hash. The difference between encryption and hash is that with an encryption-algorithm it is a 2-way process encrypt and then decrypt. MD5 being a hash is a 1-way process, there is no decryption possible.
However there are hackers,crackers or whatever you call them, they claim to get the plain text back, but you need to pay for it. however there are some websites who store the md5 hashes along with their plain texts which help you in getting the plain text back from the hashed text. !
Some of the websites are :