Decorators dynamically alter the functionality of a property or function. The ability to create decorators is part of ECMAScript, but these three decorators are unique to Lightning Web Components. @api: To expose a public property, decorate it with @api. Public properties define the API for a component.
Lightning Web Components programming model has three decorators that add functionality to a property or function. And the 3 Decorators in Lightning Web Components are
1) @api
2) @track
3) @wire