To me a biological mother is the parent that goes through pregnancy and gives birth while a biological father is the one who impregnates the mother.
So it honestly makes me cringe when in omegaverse the one giving birth gets called a dad/father or the parents who impregnated her partner gets called a mother just because their genders usually aren't associated with their reproductive role.
Of course if it's trans people then it's a different story bc calling a trans man a mother might trigger his dysphoria but then again there are irl trans men out there who do refer themselves as the mother of the child(ren) they gave birth to...
WHY DO THEY INSIST ON CALLING HIM MOM?! IT HURT SO MUCH, IT IS NOT BECAUSE HE HAS A UTERUS THAT HE SHOULD BE CALLED MOTHER