Weepholes are small openings which allow moisture to escape from building compoents. Windows have weepholes to allow moiture caught in the channels to escape and brick walls need weepholes to allow moisture to escape to. Moisture from condensation, changes in heat (dew point) water entering around frames, water entering from the roof covering above (such as overflowing gutters) and much more.
Weepholes are needed when it is neccessary to drain moiture through or away from brick cavity construction.
In brick walls the weepholes aqre located near a the base of the outer wall of brick veneer or masonry construction and at the top of wall openings (and sometimes bottom of wall openings) for ventilation and drainage purposes. Depending on the style of construction and BAL rating of the site weepholes can be a simple driled hole, a plastic or nylon sleeve, or a gap between brick purpends (between adjoining bricks).