It means that for every 180 days given, 90 days to stay and 90 days are out in schengen so if you have 5 years multiple entry then you can go back twice a year. you can have 10 times entry for 5 years. i have 1 year multiple visa and im allowed to enter 90 days in and 90 days out. im a filipina anyway. im a mathematicians and don't under estimate asians we have high educational standards as what you know. sorry if i offend you....

It means that for every 180 days given, 90 days to stay and 90 days are out in Schengen so if you have 5 years multiple entry then you can go back twice a year. you can have 10 times entry for 5 years. I have 1 year multiple visa and I'm allowed to enter 90 days in and 90 days out. I'm a Filipina anyway.