聊天 means 'to chat' or 'to have a casual conversation'. Literally, 聊 (liáo) means 'to talk idly' or 'to chat', and 天 (tiān) here is not 'sky' in the literal sense but part of the fixed compound 天, which historically derives from the phrase 聊天儿 ('chat about the sky') — an old-fashioned, playful way to refer to light, meandering talk with no serious agenda. Over time, the phrase solidified into a common verb meaning informal, friendly conversation.

This word is used frequently in everyday spoken Chinese, especially for relaxed, non-business interactions — with friends, family, or online contacts. It implies informality and mutual interest, not formal discussion or debate. You can use it with objects (e.g., 聊天儿 with someone), aspect particles (e.g., 在聊天, 聊过天), or as a noun (e.g., 一次聊天). It's neutral in register — appropriate for most social contexts, though slightly less formal than 交谈 or 对话.