MD5 is an encryption technology that produces a 128-bit hash value. The MD5 is usually calculated for files and text to prove the authenticity of the package that you have. The option you have there is actually called MD5 Check or MD5 Checksum and it tests the package against a MD5 file to see if it's original. Nowadays, the MD5 hashes are used to validate the data integrity of a file or package.