CIF stands for Crystallographic Information File and also Crystallographic Information Framework. The format is promoted and standardised by the International Union of Crystallography. See Documentation and Resources for Users and Developers of CIF Software.
The IUCr CheckCIF service can be used to check the integrity and cosistency of crystal structure encodings in CIF.
CIF files encoded with the current version should begin with the 11 bytes
#\#CIF_1.1 immediately followed by whitespace.