Computer programmers use a lot of words with special meaning in their world. The word "bug" is one of them, and by that they refer to faults in their programs. Debugging is the process of solving those faults.
The interesting thing with this word is where it comes from. It actually comes from literal authentic natural bugs.
Back in 1950's - 1970's computers used to be huge. By "huge" we mean an entire room filled with thousands of cables and transistors. In those days spiders, flies, cockroaches or other insects where getting in those rooms messing with the cables. Microchips were not yet mainstream, so there had to be many many cables and transistors for a computer to work. In order stop bugs eat the cables or other equipment, programmers had to get in the room and debug it.
Today we don't even notice how many problems this wonderful invention of microchips solves. One of them is real bugs.