"Academic" is kind of a broad brush. A professor and a teacher are both academics. One difference is tenure and research. A professor is eligible for tenure, and expected to do research or scholarship. They can train grad students.

In contrast, most undergraduate teaching is done by "adjuncts" for whom the job is essentially gig work. Moreover, professors are considered "faculty" and adjuncts "staff," making it confusing to figure out how many employees of a university are engaged in teaching versus doing other things. For instance a faculty-to-staff ratio would be misleading.

Disclosure: I was an "adjunct" many years ago.