I think "tap" - a region where metal interconnects (metals / contacts) are brought in electrical contact with wells and substrate - includes both active (diffusion, OD, moat,...) mask and n+ or p+ mask.
This forms a highly dopes silicon regions right under the contacts (or under silicide - a metal-like material formed on the top of silicon), enabling an efficient tunneling through the Schottky contact, and hence providing a low-resistive, Ohmic contact.
"Ohmic contact" is an idealization meaning that the voltage applied to the metal is "transferred" directly to semiconductor region (a quasi-Fermi potential) without any voltage loss (no voltage drop) at the interface.
Max