AngularJS has a set of built-in Directive which has HTML attributes with the prefix ng-
. Make sure your directive naming does not conflicts with HTML5 attributes like <article>, <aside> & <details> etc.
Use an unique prefix
If you use a Directive as an element, add a prefix to all elements to avoid naming conflicts with future HTML5 and possible integrations with other Libraries.
Use a unique prefix as a kind of namespace to avoid naming collision with HTML current/future elements.
A recommended and wide spread convention from the Angular community is to have two letters prefix names that identifies your Application.
Example
ng-
(from the core)ui-
(from angular-ui)
You can make unique prefix for your Application. Example, If you are developing Hotel Booking System just make name prefix hb-
.