Definition of Chat Reference Service?
Chat service is online service. You can discuss in real time. And if we talk for example about library chat, you'll get the answer immediately without waiting as by email.
One chat definition :
"Chat service refers to online, interactive, remote transactions with patrons"
(see : http://www.contrib.andrew.cmu.edu/~matthewm/survey.html )
Information of chat services and products you can find here: