The Synoptic Gospels are merely the first three Gospels in the New Testament which, according to scholars (and the OED), all share the same point of view. This grouping specifically includes:
The synoptic Gospels share a common story outline as well as similar paragraph and sentence structures, and, in some cases, the exact same words. They aren't identical -- certain sections still appear in one or two, and not in the other(s) -- but they are far more similar than any other subset of gospels. This similarity is often referred to as the synoptic problem when historians discuss evidence, hypotheses and reasons why these similarities exist.