It describes something as being in accordance with the law.
For example:
* "That is a legal document."
* "It's legal to drive at 60 mph on this highway."
You can also use "legal" as a noun in a few specific contexts, such as:
* "The legals" - referring to the legal aspects or documents of a situation.
* "The legals are being reviewed."
However, these usages are less common than using "legal" as an adjective.