They are also your 1st cousin.
Your 1st cousin's daughter is your 1st cousin once removed.
Your 1st cousin's baby is your 1st cousin once removed.
Your 1st cousin's child is your 1st cousin once removed. Your 2nd cousin's child is your 2nd cousin once removed. And so on...
If this person is your great-grandma's 1st cousin, they are your 1st cousin 3 times removed. If this person is you great-grandma's 2nd cousin, they are your 2nd cousin 3 times removed. And so on.
you call your mums cousin a 2nd cousin, because your mums cousin is her 1st cousin, wich makes your mums cousin your 2nd cousin.
Second cousin.
Your mother's 1st cousin's child is your 2nd cousin.
they are ranked as 1st cousin, 2nd cousin, 3rd cousin. 4th cousin, etc. Also as 1st cousin once removed, twice reoved, three times removed, etc. And then on to 2nd cousin once removed, etc, etc,
Your mother's first cousin is YOUR first cousin, once removed. The child of your mother's first cousin is YOUR second cousin.
Your first cousin's child's child (your first cousin's grandchild) is yopur first cousin twice removed.
Mainly because they are unfamiliar with genealogy terminology. In their mind, a child of a 1st cousin becomes their 2nd cousin when in fact the child is their 1st cousin once removed.