“Overbought” is a term used to express the value condition of an asset that has traded above a specific level.
Whenever something is classified as overbought or is in overbought territory, it is typically expected to be a good time to sell-off positions.
Overbought levels are identified through a combination of technical and fundamental indicators.
The term itself is highly subjective and varies from trader to trader; there is no one universal definitive guide for the establishment of oversold and overbought levels (the closest tool available is the RSI).