Airspeed is the speed of air relative to an aircraft. Is there a general term for this that applies to any object in any fluid (that is in motion)? For example, if a car were to be driving 10 mph into a 20mph headwind, air would be moving past it at 30mph. Saying that the car has an airspeed of 30mph seems appropriate. But what about a fish swimming in a river?
This is called relative velocity in engineering and can be applied to any body moving relative to any fluid whether it's air or water or other.
I haven't heard a specific word, but I have heard modifiers used. 10 knots with the current 10 knots against the current