In printing, ink is transferred to paper from another material, usually a metal plate or a wooden block. If the plate or block has been worked so it will receive ink in the same way each time it is applied, then there is a matrix and more than one print can be made. Before electrostatic, ink jet, and other new ways of printing were invented for use with computers, everything was printed in one of only four ways: relief, intaglio, stencil, and planographic.
The matrix, or ink-holding surface, is different for each one. In relief printing (woodcut) the ink sits on the top surface of a plate or block that has been carved. In intaglio (etching and engraving) the ink sits in the grooves. In stencil printing (silkscreen) there is a hole cut in the matrix and ink is pushed through it. In planographic printing (lithography) the matrix is flat, and the printing part is treated to hold ink, the other parts to repel it.