noun
tan line; tan lines
Refers to the visible mark or line left on the skin after sunburn or suntan, often from clothing or swimwear.
海に行ったら、水着の日焼け跡がくっきり残った。
After going to the beach, I had clear tan lines from my swimsuit.
日焼け跡が恥ずかしくて、肩が出せない。
I'm embarrassed by my tan lines and can't show my shoulders.
日焼け means sunburn or suntan in general, while 日焼け跡 specifically refers to the resulting tan line or mark.
Compound of 日焼け (sunburn) and 跡 (mark, trace).