Cousins what?

I suppose the most common error people make when understanding their relationship with other members of the family is calling their cousin's child a second cousin.  Your cousins child is you 1st cousin once removed (1C1R) as can be seen from the chart below.  

Whether you are a 1st, 2nd or 3rd cousins is calculated by your relationship to the common ancestor.

I hope this chart helps you to understand where you fit in in relation to others.