Google Wave is an online tool for real-time communication and collaboration. "A wave can be both a conversation and a document where people can discuss and work together using text, photos, videos, maps, and more. It can be used as a personal communication tool. It is designed to merge e-mail, instant messaging and social networking."
"Google Wave works like systems such as e-mail but instead of sending a message along with its entire thread of previous messages, or requiring all responses to be stored in each user's inbox for context, message documents (referred to as waves) that contain complete threads of multimedia messages (blips) are perpetually stored on a central server. Waves are shared with collaborators who can be added or removed from the wave at any point during a wave's existence."
A wave is a conversation with several participants who are added to a wave to discuss the information and content. In order to participate in google wave you have to apply for or receive an invitation.Read what Mashable says about google wave: