Bully beef is a type of canned meat that is made by cooking beef and then canning it with some sort of preservative, such as salt or vinegar. The reason it is called "bully" beef is because the word "bully" used to mean something that is good or excellent, so bully beef was originally a really good quality type of canned meat.
Nowadays, bully beef is often made from lower-quality cuts of beef that have been heavily processed and canned to make them last longer. Some people really like bully beef because it can be eaten cold and doesn't require refrigeration, which makes it a convenient food to take on camping trips or to eat in situations where refrigeration isn't available.
However, some people think that the taste and texture of bully beef isn't very good, and that it is a bit tough and chewy. So, while some people enjoy it, others don't like it very much!