Meaning of B64 in English
Base 64 extension file
A b64 encoding get an 8-bit data file and convert it to an ASCII data file.
This encoding is mainly applied to DER and BER encoded contents; in this way it is possible to have a simple, friendly (ascii) representation of the content itself.
The encoding is done taking the data content in groups of 24 bits, 3 bytes at a time, and putting them into 4 bytes: the original information of the first 3 bytes are stored in the first 6 bits of this new 4 bytes (4 bytes x 6 bits = the 24 original bits)!
Acronyms Misc English vocab. Словарь сокращений и аббревиатур английского языка. 2012