What is a second cousin twice removed??

What is a second cousin twice removed??
I remember it this way. First cousins own two grandparents in adjectives. Second cousins have two great-grandparents surrounded by common. A second cousin once removed would be the child of your second cousin. A second cousin twice removed would be the grandchild of your second cousin.
I suppose in recent times a single grand or great-grandparent would suffice to qualify as a cousin or second cousin as long as nearby is a direct blood line to the human being involved.
A cousin you can f*ck and not feel guilty...