Definition of rock martin in US English:

rock martin

noun

  • Any of several martins and swallows that frequent cliffs, rocky outcrops, etc.; specifically (originally) the crag martin, Ptyonoprogne rupestris, or (in later use) the dark brown P. fuligula of Africa, which also nests on man-made structures.

Origin

Mid 19th century; earliest use found in The Penny Cyclopaedia.