A shill is a person who publicly promotes or praises something or someone for reasons of self-interest, personal profit, or in the case of companies, for the benefit of the product or organization they represent. The term originated from carnival and circus slang, where a shill would be a plant in the audience, pretending to be an enthusiastic independent customer to entice real customers.
Shilling is also a term used in online communities to describe the act of endorsing a product, service, or viewpoint under the guise of sincerity, but where the individual has a vested interest. It is often viewed negatively, especially when it is done deceptively.
As a term, it can also apply to financial markets. For example, in cryptocurrency communities, a shill might excessively hype a particular coin or token with the aim of increasing its price or attracting buyers, often while concealing their own ownership or interest in the asset. This usage has grown with the rise of social media, where such behavior can be widely disseminated.