I've seen the hyphen (
-) used in phrases a lot, for example:
When and why is the hyphen used, and what does it mean when it's used?
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That's a hyphen. They notify the reader that two or more elements in a sentence are linked.
Rule 1. Generally, hyphenate two or more words when they come before a noun they modify and act as a single idea. This is called a compound adjective.
an off-campus apartment
When a compound adjective follows a noun, a hyphen is usually not necessary.
The apartment is off campus.
There are several rules. Have a look at this.