Mom is what many Americans call their mothers. Mothers with young children hear this word about 10,000 times a day, usually all in a row. Mom. Mom. Mom. You get the idea.
Mom is a very common informal word in the U.S. for “mother,” shortened from momma or mommy, an even more childish nickname for your mother. If you’re talking directly to your mom, using “mom” like a name, capitalize it – “Hi, Mom!” If you’re talking about her or another mom, don’t – “Hi, other person’s mom.” In other English-speaking parts of the world, people might use mum instead.