I have been trying to learn for awhile now what cousin once removed, aunt once removed etc. means and I think I have finally got it down.
It is how many generations away from you it is. Once removed means a difference of one generation, twice removed means a difference of two generations. If your first cousin has a child, this child is your first cousin once removed.
The chart below is like an easy cheat sheet for you.
This link has more very useful information from Ancestry.
