There are hundreds of online glossaries out there. Here are a few that you may want to start with.
NetSmartz is a Web-based educational resource from the National Center for Missing and Exploited Children focused on Internet safety. They provide a comprehensive Internet Definitions page for parents and educators.
OnGuard Online provides users with a number of practical tips and tools from the federal government and the technology industry for safe Internet use.
i-SAFE Inc. is a nonprofit foundation dedicated to providing of Internet safety education by means of a classroom curriculum and community outreach for students, teachers, parents, and law enforcement. On their site, i-SAFE provides a glossary to give users better knowledge of computers, Internet-related language, and specific i-SAFE terms and processes. i-SAFE also provides parents and educators with a listing of chatroom shorthand, including both abbreviations and emoticons.
The National Center for Missing & Exploited Children has compiled a comprehensive listing of chatroom shorthand, often used by kids and teens as they communicate online.