What are these bin files?

In the MySQL directory, I see several very large bin files named {aaa}-bin.00001 through .00005. {aaa} is just the same three letters. I also see mysql-bin.00117 and .00118. that are smaller, about half the size. They have recent datetime stamp with 24 hours. I have no idea what the large old ones are for and if they can be deleted. I same some small ones {aaa}-relay-bin.00064 and .index. I am doing replication.