A hardness test is topically performed by pressing a specifically dimensioned and loaded object (indenter) into the surface of the material you're testing. The hardness is determined by measuring the depth of the indenter penetration or by measuring the size of the impression left by an indenter.
Hardness tests that measure the depth of the indenter penetration include: Rockwell, Instrumented Indentation Testing and Ball Indentation Hardness.
Hardness tests that measure the size of the impression left by the indenter include: Vickers, Knoop and Brinell.