From Sheldon Brown:

Braze-on
A small fitting permanently attached to a frame. On traditional steel frames these attachments are held on by brazing, but the term "braze-on" is also used for fittings that are welded, glued, rivetted or moulded on to frames of other materials. Typical braze-ons would include cable stops and guides, water bottle cage mounts, shift lever bosses, cantilever brake bosses and cable stops, pump pegs, etc.