Basic Definition:
Timing, exposure, and exposure time are names used by different manufacturers to describe a similar concept. The exposure time is the length of time that the detector is exposed to photons to collect one image frame. Exposure time is the same as 1/(# frames per second).
More Information:
While increased exposure time can improve signal to noise ratio up to a point, it will eventually result in detector saturation. If all other factors are kept constant, frame averaging can theoretically achieve the same SNR improvement as increased exposure time, but without the risk of detector saturation. The effective exposure will be (exposure time) x (# of frame averages).