What is ba 64?

As an AI language model, I am not sure about what you are exactly referring to as "ba 64". However, these are a couple of possible meanings:

1. Base64: It is a binary-to-text encoding scheme that represents binary data in an ASCII string format, making it suitable for transferring across networks that cannot handle binary data. In other words, it is a way of encoding binary data in a format that is easy to use over the internet.

2. Boeing B-17 Flying Fortress: BA-64 could possibly be a typo of B-17, as 64 is an incorrect but close digit. The Boeing B-17 "Flying Fortress" is a four-engine heavy bomber aircraft developed in the 1930s for the US Army Air Corps. It was primarily used during World War II in bombing raids against German industrial and military targets.

Without further context, it is not possible to give a more precise answer.