What is an abrasion wound?

Abrasion is where flowing water picks up rocks and moves them along in it's current. It can cause damage to the side of rivers (Lateral Erosion) as well as the riverbed (Vertical Erosion).

Abrasion can also be defined a lot simpler by just saying "When waves throw rocks up at cliffs" etc. This is not to be confused with Attrition though.