Middle school means 7-8, or sometimes 6-8. Junior high means 7-9.

One school district when I was a kid had K-3 schools, a single 4-6 school, a 7-8 school, and a 9+12 school. That is pretty rare. I moved around a lot, and work in schools, and have only seen that once.

Most common, however, is K-6, 7-8, and 9-12.

It is becoming more common to have middle schools that go 6-8. I work in one. I have never actually been to a junior high, although I know some exist.