INT 03h (3)              Breakpoint

INT 3 is the breakpoint interrupt.

Debuggers use this interrupt to establish breakpoints in a program
that is being debugged.  This is normally done by substituting an INT
3 instruction, which is one byte long, for a byte in the actual
program.  The original byte from the program is restored by the
debugger after it receives control through INT 3.

INT 03h (3) Breakpoint