matching is the process of indentically eqauivalent the electrical parameter of the device, mostlt transistor...
LEt say in the layout u got 2 transistor symetry to each other, it's better if the transistoris matched, for example...the resistive of both transistor is equal....
Done by nmany thechnique like common centriod, and etc..
Matching is done for best signal transfer, and ease in analysis