Rowing stroke

In rowing, the stroke is the action of moving the oar through the water in order to propel the boat forward. The two fundamental reference points in the stroke are the "catch" where the oar blade is placed in the water, and the "extraction" (also known as the 'finish', 'release' or 'tapping down') where the oar blade is removed from the water. After the blade is placed in the water at the "catch", the rower applies pressure to the oar levering the boat forward which is called the "drive" phase of the stroke. Once the rower extracts the oar from the water, the "recovery" phase begins, setting up the rower's body for the next stroke.
Stages of a stroke.
Drive.
The drive is the phase from the catch to the extraction.
Recovery.
The recovery follows the drive and returns the oar and the rower from the point of extraction to the catch.
Sweep vs sculling.
Sweep rowers (one oar per person) and scullers (two oars, one in each hand) have similar stroke styles, with some differences to accommodate the number of oars held by the rower. The most notable difference is that the oar handles overlap in sculling at the midpoint of the drive, and again during the recovery. This requires the sculler to cross one hand over (left over right) and/or in front of the other hand to avoid the oar handles colliding. While sculling is a fully symmetrical movement (with exception of the handle overlap), sweep oar rowing is slightly asymmetrical and many rowers strongly prefer one side to the other.
Also, sweep oar rowers usually feather and square the oar with the inside hand (the one closer to the rowlock), allowing the handle to turn within the outside hand, whose wrist remains flat throughout. This is obviously not possible in sculling, and scullers tend to feather and square by holding the oar handle in the extended fingers when feathered, and rolling it into the palm of the hand to square it, the wrist remaining flat throughout. 
The average speed of a boat increases with the crew size and sculling boats are slightly faster than the equivalent sweep boats.
Local differences.
The rowing stroke differs slightly depending on location and coaching technique and especially the coach. Differences (especially between experienced rowers) are only marginal and can often only be seen by detailed video-analysis. For example, sometimes the Canadian eight team used a style where the body was swung more during the drive.