# Identifiers

> For the complete documentation index, see [llms.txt](/llms.txt)

Identifiers are names used for variables, functions, types, and other entities. They must start with a letter or an underscore and can contain letters, digits, and underscores.

```motoko no-repl
let name = "Motoko";
let a1 = 123;
let camelCaseIdentifier = "best practice";
let snake_case_identifier = "for compatibility with other languages";
```

## Reserved syntax keywords

Motoko reserves [keywords](https://docs.motoko.org#keywords) for its syntax and they cannot be used as identifiers.