Knowledge that comes from interacting directly with the world. A-posteriori knowledge is that which, in a Marxist sense, is assembled by the struggle of an individual with their material conditions, subject to their own personal psychological makeup. A-posterior knowledge comes from direct observation and from logical connections made between direct observations.
For instance, knowledge of the redness of a specific apple is a-posteriori knowledge; knowledge that “apples tend to be red” is an axiomatic deduction from many specific instances, another form of a-posteriori information.