period can mean one instance of a woman's menstrual cycle
, that is, one month starting from the onset of bleeding to the onset of the next month's bleeding, but most often the word period
when used in this context means only the portion of the cycle
in which the woman
There are all sorts of colourful slang terms for this, such as being on the rag, having a visit from Aunt Flo, seeing red, or the blessedly accurate 'bleeding', which I happen to favour. See euphemisms for menstruating.