Our online medical glossary of medical terms and definitions includes definitions for terms related to treatment, and general medicine
1. The lapping of one thing over other; as, an overlap of six inches; an overlap of a slate on a roof.
2. An extension of geologicalbeds above and beyond others, as in a conformable series of beds, when the upperbedsextend over a wider space than the lower, either in one or in all directions.
Source: Websters Vocabulary