For example, you can just post a comment for which you expect no response, or you can send a message and wait to see if someone responds. Sometimes it is nice not to wait. Interacting directly with another person or persons is synchronous interaction.
Synchronous interaction can also occur over the web.
Chat rooms are a great example. In is a web site which provides synchronous communication tools and is focused on teacher development. Tapped In requires a little practice, but it can be a great experience. In Any interested teachers are strongly encouraged to tour Tapped In and log in as a guest to see what is available.