Asynchronous or Synchronous?

What do I mean by these two words?  What, if anything do they have to do with learning?  If you choose to train someone online, your environment can be asynchronous, synchronous or a combination of both.  This is what each of them means.

Asynchronous – Participate in the class on their own time schedule.  The instructor or trainer may have requirements of specific deadlines that need to be met, such as a discussion board posted by a certain date or time.  Students do not have to be be online at a specific time to participate in the class.

Synchronous – In order for students to participate in the class they have to be online a specific time.  This style of training may call for something like a video conference or a live audio session that students can participate in.  The advantage of this is live interaction.  The disadvantage of this format is that students are bound by a very specific schedule and access to a computer at that specific time.