"High surf" refers to large, powerful waves in the ocean or sea. It means the waves are bigger and stronger than usual, potentially causing dangerous conditions for swimmers or surfers. Full definition
Be careful of slippery rocks and do not attempt this in high surf. (parrishkauai.com)
However, the rate of erosion displayed in the video is obviously excessive given the relative calm weather and lack of high surf. (dotearth.blogs.nytimes.com)
Look for waist - chest - shoulder high surf at exposures, while standout spots see sets head high range. (santa-teresa-surf-report.com)