Definition of "spotter"

A person who observes something.  examples

A member of a sniper team who in addition to this function is responsible for providing additional information about targets from a different point of view.  examples

(weightlifting, gymnastics, climbing) One who supervises a person performing an activity, in order to help them should they be unable to complete it.  examples

(US) A person who gives directions for a crane or vehicle (that is challenging to navigate) from a different point of view to the moved load.  examples

Dolphins of the genus Stenella, and specifically Stenella attenuata distinguished from the streaker (Stenella coeruleoalba) and the spinner (Stenella longirostris).  examples

(motor racing) A team member responsible for communication with the driver to keep them up-to-date about on-track events, such as other nearby cars.  examples