어머니 vs 어머님
I was reading a study help and it said 어머니 means Mother (one's own, plain), but 어머님 means Mother (someone else's, honorific) or Mother-in-law (one's own, honorific).
So m question is, when talking about your own mother, do you still use 어머님? Or should you say 어머니?
And does 어머님 mean "mother-in-law" as well as "mother"?