Proofing - Soft
Soft-proofing is the simulation of how a printed piece will look using a computer screen. In contrast to a "hard-proof", a soft-proof uses a computer, display and software (hence the name) to show the brightness and color of a printed piece. Commonly, the intention is to approve the look of the image before it gets printed, so that the waste of having to reprint an image can be eliminated.
While it is theoretically possible that a particular computer monitor might, by coincidence, match the look of a particular printer's output, generally it is required that the user have a calibrated and profiled monitor, a profile representing the printing state of the printer, and software that will make use of these profiles to adjust the colors on-screen.