used as a GREETING when you meet somebody, when you answer the telephone or when you want to attract somebody's attention:
Hello John, how are you?; Hello, is there anybody there?; Say hello to Liz for me; They exchanged hellos (= said hello to each other) and forced smiles.
MORE ABOUT greetings
• Hello is the most usual word and is used in all situations, including answering the telephone. • Hi is more informal and is now very common. • How are you? or How are you doing? (very informal) often follow Hello and Hi: ‘Hello, Mark.’ ‘0h, hi, Kathy! How are you?’ • Good morning is often used by members of a family or people who work together when they see each other for the first time in the day. It can also be used in formal situations and on the telephone. In informal speech, people may just say Morning. • Good afternoon and Good evening are much less common. Good night is not used to greet somebody, but only to say goodbye late in the evening or when you are going to bed. • If you are meeting someone for the first time, you can say Pleased to meet you or Nice to meet you (less formal). Some people use How do you do? in formal situations. The correct reply to this is How do you do?