The act of listing pertains to the offering of an exchange of trading pairs for a specific asset. Within the context of traditional markets, listing refers to shares of companies or material assets that are at hand to be traded within that specific stock exchange.
The company that had been listed had gone through and passed regulatory markers making it viable to be bought. Being listed means the company or asset shares are at a base threshold of quality.
Within cryptocurrenies, listing would refer to the coin being listed alongside Bitcoin or any of the major exchange pairs. What this tells crypto traders is that there is enough liquidity in the associated trading pair to come up with price discovery that is accurate.