Vee brakes (sometimes spelt v-brakes) are also known by their technical name, linear pull cantilever brakes. They were designed for mountain bikes as a performance improvement on cantilever brakes but have since become standard on many hybrids and some touring bikes and folding bikes.
They are inexpensive and moderately easy to set up and maintain. A well set up vee brake provides excellent stopping power.
Vee brakes require vee brake levers; they are incompatible with levers designed for cantilever brakes or caliper brakes, such as standard drop bar levers.
There can be compatibility issues between vee brakes and pannier racks if both need fixing to the stays at the same point. This is a common problem on small frames. A work-around is to fix the rack to a seatpost clamp that is designed as a rack fixing point. Another solution is to change to cantilever brakes.