A
triple junction is the point where the boundaries of three
tectonic plates meet. At the triple junction each of the three boundaries will be one of 3 types - a
ridge (R),
trench (T) or
transform fault (F) - and triple junctions can be described according to the types of plate margin that meet at them (e.g. Transform-Transform-Trench, Ridge-Ridge-Ridge, or abbreviated F-F-T, R-R-R). Of the many possible types of triple junction only a few are
stable through time ('stable' in this context means that the geometrical configuration of the triple junction will not change through geologic time).