* 학원 (hagwon): This is the most common term and refers to a private educational institution, often for after-school tutoring or test preparation. This is likely what you mean if you're thinking of a cram school or tutoring center.
* 아카데미 (akademi): This is a loanword directly from English and is used for institutions that are more prestigious or focused on a specific area of expertise, like a film academy or a military academy. It carries a more formal connotation than 학원.
* 대학원 (daehakwon): This means "graduate school" and could be considered an "academy" in the sense of a higher education institution focused on advanced study.
* 학회 (hakhoe): This refers to a learned society or professional association, sometimes having an academic focus.
Therefore, to choose the best term, you need to specify what kind of academy you're referring to. For most common uses, 학원 (hagwon) is the appropriate word.