chatとは何ですか?To converse in an easy, familiar manner; talk lightly and casually.Computer Science To participate in a synchronous exchange of remarks with one or more people over a computer network.An informal, light conversation.Computer Science A synchronous exchange of remarks over a computer network.Any of several birds known for their chattering call, as of the genera Saxicola or Icteria.chat up To engage (someone) in light, casual talk: "He would be . . . chatting up folks from Kansas” ( Vanity Fair).