Erosion – The wearing away and removal of material by turning it into a solution or by attrition, abrasion or hydraulic action

So river abrasion is wearing down and grinding down a river's bed and banks.

Types of erosion:

Solution: The sides of the river dissolve into the water.

Attrition: Wearing down the river bed by bouncing into the sides of the river and breaking off particles.

Abrasion: Wearing down the river bed by grinding, rubbing, scratching and scuffing like sandpaper.

Hydraulic Action: The force of water against riverbanks compresses air into cracks, which expands and fractures the rock over time.