What are classes of identifier?

What are classes of identifier? Explain each class with an example i.e. regular and delimited identifier.

There are two classes of identifier. These identifiers must contain 1 to 128 characters.

1. Regular identifiers: They follow the rules for the format of identifiers. They are not delimited when used in transact SQL statements.

Example:
Select * from table_name Where ID =110

2. Delimited identifiers: They follow the rules for the format of identifiers. They may or may not be delimited when used in transact SQL statements. They are enclosed either in (“) or ([])

Example:
Select * from [table_name] Where [ID] =110
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