Linked from
The 5 pages that link to Standup paddleboarding, each with the reason it gives.
CanoeCompared with: It uses a board and standing stance rather than a seated, enclosed canoe hull.
WindsurfingCompared with: It uses human-powered strokes instead of wind-driven propulsion.
KayakingCompared with: It uses a standing posture and a different paddle instead of a kayak cockpit.
SurfboardCompared with: Its larger board can ride waves, but paddling with an oar defines the sport.