What is the full name of BUG? What is the source?

The original meaning of the word bug is "bug" or "worm". But now, if there are some undiscovered defects or problems hidden in a computer system or program, people also call it "Bug".

The first generation of computers were made of many large and expensive vacuum tubes, and used large amounts of electricity to make the tubes glow. It may be that the light and heat generated by the operation of the computer attracted a small bug? Bug to get into a vacuum tube, causing the entire computer to fail to work. It took the researchers half a day to finally discover the cause. After taking the little bug out of the vacuum tube, the computer returned to normal. Later, the term bug was used to refer to hidden errors, defects, loopholes or problems in computer systems or programs.