四本線黒セーラー とはどういう意味ですか?

質問を翻訳

I'm not sure but maybe…
In Japan, in many junior high schools and high schools, students wear school uniforms.
For girl's uniforms, "sailor suit" style is very common, and the colors of the fabric and of the lines on the collar are different by school ( in each school ),
and the number of the lines also.
White lines on black ( navy ) fabric is the most popular.

四本線＝four lines 黒＝black セーラー＝sailor suit
So its meaning is "a black sailor suit with four lines on the collar", I think.