Girlfriend said that my underwear can be called knickers?

a girlfriend calls the type of underwear i wear knickers. i'm meaning boys high cut knickers with a thin bit of elastic round the sides,not girls type. i'm used to her saying to me get your knickers on, or something. now i've started calling them knickers too. do many girls use this term for boys underwear? she said they can be called that, and said it sounds more cute with me? what does she mean?