SHA (Secure Hash Algorithm) is an algorithm and it is mainly used to verifying integrity of files under linux. Unlike MD5 (it is only 128 bits), SHA uses 160 bits by default (SHA1) and there is 4 another improved version:
sha224: 224 bits
sha256: 256 bits
sha384: 384 bits
sha512: 512 bits
You can learn sha1 sum of a file (160 bits) with:
sha1sum filename
or
shasum -a 1 filename
shasum uility takes -a parameter as 1, 224, 256, 384 and 512 repectively and make calculations for the specified bits length.