Formal:
* 您好 (nǐ hǎo): This is the most common and polite greeting, suitable for almost any situation. It literally means "you good," and is used for strangers, elders, and people in positions of authority.
Informal:
* 你好 (nǐ hǎo): This is also commonly used, but is slightly less formal than 您好. It can be used with friends, family, and people you know well.
* 嗨 (hāi): This is a more casual greeting, similar to "hey" in English. It's appropriate for friends and people your own age.
* 喂 (wèi): This is used to get someone's attention, similar to "hello" in English. It can be used in both formal and informal situations.
Other greetings:
* 早上好 (zǎo shàng hǎo): Good morning
* 下午好 (xià wǔ hǎo): Good afternoon
* 晚上好 (wǎn shàng hǎo): Good evening
Remember that the tone of voice and body language can also affect the meaning of a greeting.