Frame

A frame is a still image. Video is made up of many frames per second to create the illusion of movement.
The number of frames to be displayed per unit of time is expressed in frames per second (fps) or Hertz (Hz). These are different terms for the same measurement.

Types

Digital video compression techniques involve compression of frames:

I-frame

A full 'Intra-coded picture'

P-frame

'Predicted' from previous frame(s)'s picture

B-frame

'Bi-predictive' or 'Bidirectional' calculated from surrounding frames's pictures. Can painlessly be skipped.