How to determine Docker version

Question

If I run:

$ docker -v

the result is:

Docker version 18.06.1-ce, build e68fc7a

When they say "version," what do they mean?

If you use Docker 1.13 or higher, use --cpus instead.

I'm curious since the difference between 18 and 1 seems excessively large to me. Is the doctor really that old? Or are the docker versions increasing at such a rapid rate?