To correct a problem in hardware or software. Debugging software means locating the errors in the source code (the program logic). Debugging hardware means finding errors in the circuit design (logical circuits) or in the physical interconnections of the circuits.
Sometimes You Need a Hammer!
Many years ago, in order to find a bug in the Windows version of this encyclopedia, the text had to be scrolled until it crashed. Rather than holding the mouse button down for several minutes, the hammer did the job. Were there more sophisticated methods? Of course, and a built-in auto scroll was later added. Two-pound hammers are not normally part of the debugging toolkit.