Chat:
An online, real-time interactive communication method using text to send and receive instant messages. From: www.worldwidelearn.com/elearning-essentials/elearning-glossary.htm

Two or more individuals connected to Internet have real-time text-based conversations by typing messages into their computer. Groups gather to chat about various subjects. As you type, everything you type is displayed to the other members of the chat group.
From :www.tamu.edu/ode/glossary.html