“Keep in touch!”

One of the students at your English language school is moving back to his home country. Some of the students contributed to buy him a gift. On the card for the gift, you want to write a nice, friendly message. You write:

Keep in touch!

Keep in touch!

This is a common phrase to use when you're permanently saying goodbye to someone, like when you leave a job, graduate from a school, or move to another city. 

To "keep" doing something means to continue to do it. Being "in touch" means that you communicate with someone. So "Keep in touch!" means "Continue to communicate with me!"

However, "Keep in touch!" is such a commonly-used phrase that it often doesn't mean anything. If someone tells you to "Keep in touch", they probably don't actually expect you to call or email them. If you really do want to keep in touch with someone, you might need to say or write it in a different way like this:

Let's definitely keep in touch.

In written notes, emails, etc., you can also write "K.I.T" as an abbreviation of "Keep in touch".