1. What does it mean?
스압 abbreviates 스크롤 압박, literally scroll pressure. It warns that a page contains a long stretch of text, many photos, or both.
Also written or said as 스크롤 압박, seuap
2. The nuance
It describes length, not necessarily complexity or a problem loading the page. Writers often put 스압 or 스압주의 near a title as a courtesy.
3. Examples
“여행 사진이 많아서 제목에 스압주의라고 썼어.”
There were so many trip photos that I put a long-scroll warning in the title.
“스압이지만 정리표가 있어서 필요한 부분을 찾기 쉬워.”
It's long, but the summary table makes the relevant part easy to find.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.