Single-step

To single-step a program is to have it execute a single instruction, and then halt, so that the programmer can see what the program is doing.

There are a number of different ways to cause single-stepping: on older computers with front panels, there is usually a switch setting which allows single-stepping the CPU. On newer machines, there is usually some way to cause the CPU to execute a single instruction, and then trap; debugger software then takes control, and allows the same sort of examination.