He says I’m his bitch ?? My boyfriend

What does it mean when my boyfriend of a year and a half always says I’m his bitch especially mostly when we have sex?? What does it mean? Like Im his woman?

Does your boyfriend or husband say this? Is it good or bad never had a man say that to me before this man.

Tia ladies!!

Ps I’m not young in my early 30’s he’s older forty something lol