Question

what is mean by menstans cycle

Answer 1

there is no thing menstans cycle

Answer 2

The average menstrual cycle length (cycle length being from the start of one period until the day before the next flow) in many studies, and from many countries, is about 28 days, or a lunar month. However, "regular" has two possible meanings:

How many days long is a normal menstrual cycle (how short is too short, and how long is too long)? and
How variable in length, from one cycle to the next or over a year, is normal