What the 90/180 rule means
For many short-stay visitors, time in the Schengen Area is limited to 90 days in any rolling 180-day period. The count is not simply reset at the start of a calendar year. Each day of a trip can look back across the previous 180 days.
The rule is separate from whether you need a visa, ETIAS or another authorisation. A traveler can be visa-exempt and still need to stay inside the short-stay day limit.