It's the difference in number of generations from the common ancestor. Foro has one more generation in his lineage than I do.
A simpler example: You have first cousins (probably). Your common ancestor with them is your grandparents. Now let's say you have a child. Your child is a first cousin once removed to your first cousin, because the common ancestor is the same but there's now one more generation leading to your child. I hope that's clear.
An edit to make things a bit clearer, hopefully: Let's say your first cousin also has a child. Now your child and your cousin's kid are second cousins to each other, because the common ancestor is 3 generations back from both of them. And when your cousin's kid has a kid of his own, that little one will be a first cousin twice removed to you, and a second cousin once removed to your child.
A simpler example: You have first cousins (probably). Your common ancestor with them is your grandparents. Now let's say you have a child. Your child is a first cousin once removed to your first cousin, because the common ancestor is the same but there's now one more generation leading to your child. I hope that's clear.
An edit to make things a bit clearer, hopefully: Let's say your first cousin also has a child. Now your child and your cousin's kid are second cousins to each other, because the common ancestor is 3 generations back from both of them. And when your cousin's kid has a kid of his own, that little one will be a first cousin twice removed to you, and a second cousin once removed to your child.