iChat is a combo communications program that does three things:
Instant messaging. If you don't know what instant messaging is, chances are there's a teenager near you who does.
It's like live email. You type messages to friends and colleagues in a chat window, in real time, and they type replies back to you. Instant messaging can be a great way to converse with the privacy of email and the immediacy of the phone.
In this regard, iChat is a lot like AOL's popular Instant Messenger (AIM) and Buddy Chats. In fact, iChat lets you type back and forth with any of AIM's 150 million members (it speaks the same "chat" language), which is a huge advantage. But iChat's visual design is pure Apple.
Free long distance. If your Mac has a microphone, and so does your buddy, the two of you can also chat out loud, using the Internet as a free long-distance telephone. Wait, not just the two of you—the ten of you, thanks to Tiger's beefed-up audio conferencing features.
Free videoconferencing. iChat's old name—and still its full name, as it appears in the About box—is iChat AV, where AV stands for audio-video. If you and your buddies each have broadband Internet connections and a FireWire camera—like Apple's own iSight camera, or (if your Mac has a G4 or G5 chip) even a digital camcorder—up to four participants can join in video chats, all on screen at once, no matter where they happen to be in the world. This arrangement is a jaw-dropping visual stunt that can bring distant collaborators face-to-face ...