An abbreviation of '100-yen shop'; used to refer to stores, sections, or items where goods are sold for 100 yen.
今日は１００円均一で掃除用品をいくつか買った。
Today I bought some cleaning supplies at the 100-yen section/shop.
このお菓子は１００円均一コーナーに置かれている。
These snacks are placed in the 100-yen section.
１００円均一（＝１００円均一ショップ）なら、文房具も安く手に入る。
At a 100-yen shop (i.e. 100-yen store), you can get stationery cheaply.