GOP, adaptive GOP
GOP(Group Of Pictures) - in terms of video encoding, it's several frames from one I-frame (including it) to the next I-frame.
In general, the larger GOP size provides more efficient encoding. Sometimes GOP size may be restricted by some transmitting and storing standards.
Adaptive GOP - GOP structure and size of which are not constant and settled adaptively to video content.
Open GOP - GOP which started from B-frames in display order (B-frames have negative POC values). As an example, you can look into Sony and Panasonic LongGOP standards.
Closed GOP - GOP which started from I-frame in display order.