Meaning: Serve people in a restaurant
Example: They have two people WAITING ON each table.
Meaning: Sell goods in a shop
Example: He WAITS ON customers in an electronics store.
Meaning: Provide someone with everything they need or want
Example: He has a butler who WAITS ON him.
Meaning: Wait for a result before being able to make a decision
Example: They're WAITING ON the results of the vote before taking a final decision.