Loanword from English, referring to a middle school (typically grades 6–8 in the US). Used in contexts discussing foreign education systems or international schools.
アメリカでは、ミドルスクールは6年生から8年生までです。
In the US, middle school is from 6th to 8th grade.
Variant with interpunct; less common in running text.
Borrowed from English 'middle school'.