License
Legal permission defining how a creative asset may be used, distributed, or modified.
In practice
A license is the legal permission that states how an asset such as a font, photo, icon set or piece of music may be used: in which projects and media, by how many people, and whether it may be modified or resold. Designers check licenses before use, because a font licensed for desktop printing may not cover embedding it in an app or on a website.
Often confused with copyright
Copyright is the owner's right in a work; a license is the specific permission the owner grants others to use it.
Try this
Look up the license of a free font you use and note whether it allows web, app and commercial use.