What is a spy and what do they do

An agent employed by a state to obtain secret information, especially of a military nature, concerning its potential or actual enemies.

One employed by a company to obtain confidential information about its competitors.

One who secretly keeps watch on another or others.

An act of spying.

A spy is a (military) a secret agent hired by a state to obtain information about its enemies or by a business to obtain industrial secrets from What is a spycompetitors

•  a secret watcher; someone who secretly watches other people; "my spies tell me that you had a good time last night"
• a spy is - to catch sight of
• a spy will watch, observe, or inquire secretly
• a spy secretly collects sensitive or classified information; engage in espionage; "spy for the Russians"