Question

what do you mean by menstrual cycle

Answer 1

the uterine wall in female prepares itself to receive the developing fertilized eggs. in case there is no fertilization, the thickened lining of the uterus wall break down and goes out of the body along with the blood.this is called menstruation.
the repetation of this after every month is called menstrual cycle.

Answer 2

it is a naturally occurring natural cycle.

hope this may help you