While debugging the Mark II, Hopper encountered an issue caused by a moth that had become trapped between the contacts of a relay in the computer. She carefully removed the moth and taped it into her logbook, along with the notation: "First actual case of bug being found."
This incident popularized the term "computer bug" to refer to any type of fault or error in a computer system or program. Today, the term "debugging" is commonly used in the field of computer science to describe the process of identifying and fixing errors in software or hardware.
Grace Hopper's significant contributions to the field of computer science and her pivotal role in discovering the first computer bug have made her an iconic figure in the history of computing.