In British English, these () are called brackets.
Example: The meeting (which was delayed) will start soon.

In American English, they’re called parentheses.
Example: The meeting (which was delayed) will start soon.

Now, if you add [] or {}, things get trickier:

• [] are called square brackets in both British and American English.
• {} are called braces in American English, and curly brackets in British English.

It’s a small difference, but important if you want to sound clear!