Definition: "Hello!" or an equivalent greeting.
Example:

Definition: To greet with "hello".
Example:

Definition: A greeting (salutation) said when meeting someone or acknowledging someone’s arrival or presence.
Example: Hello, everyone.

Definition: A greeting used when answering the telephone.
Example: Hello? How may I help you?

Definition: A call for response if it is not clear if anyone is present or listening, or if a telephone conversation may have been disconnected.
Example: Hello? Is anyone there?

Definition: Used sarcastically to imply that the person addressed or referred to has done something the speaker or writer considers to be foolish.
Example: You just tried to start your car with your cell phone. Hello?

Definition: An expression of puzzlement or discovery.
Example: Hello! What’s going on here?