I got a multiple-entry, short-stay, category “C” Schengen States “D” visa valid for 1 year with a duration of 90 days.
a) Does the 90-day thing in a one-year period mean that I can freely spread out my travel dates throughout that one year? For example, visit Germany in January for 21 days, come back again in April for another 21 days then in August for 21 days and finally in October for the last remainder of the 90 days?
b) Or does it mean that once I enter the Schengen area, my 90 days start counting down? For example, if I enter Germany on the 1st of January then my visa expires after 90 days (in March) regardless of whether I stayed in Germany throughout those days or not?