People who share the same grandparents are 1st cousins; people who share the same gr. grandparents are 2nd cousins; people who share the same gr. gr. grandparents are 3rd cousins;
people who share the same gr. gr.gr. grandparents are 4th cousins.
The people who fall within thoseboundaries are "removed": for example your gr. gr. grandmother is my gr. grandmother... that would make us 2nd cousins once removed. (that could be explained that your mother and I share the same gr. grandmother there by 2nd cousins and you are 1 more generation after that...)
From genealogy.com:
When the word "removed" is used to describe a relationship, it indicates that the two people are from different generations. You and your first cousins are in the same generation
(two generations younger than your grandparents),
so the word "removed" is not used to describe your relationship.
The words "once removed" mean that there is a difference of one generation.
For example, your mother's first cousin is your first cousin, once removed. This is because your mother's first cousin is one generation younger than your grandparents and you are two generations younger than your grandparents. This one-generation difference equals "once removed."
Twice removed means that there is a two-generation difference.
You are two generations younger than a first cousin of your grandmother, so you and your grandmother's first cousin are first cousins, twice removed.
