Lightning component encapsulates its even driven functionality, markup and CSS into single reusable functional units called lightning bundle (component , controller , helper , css , renderer , design , svg and documentation) . Using the bundles you can assemble it to larger components or into a complete enterprise application. By adding a appHostable tag you can expose your component to salesforce1 mobile application. You can also expose you component to lightning app builder by adding flexipage:availableForAllPageTypes to your component.
The lightning app builder allows developer and non-developer to drag and drop your lightning components to build enterprise grade applications and easily push it production with out having to write unit test code.
As a whole lightning component is a power pack to build your enterprise application on top of it.
Checkout this lightning components Trail head
See Lightning developer guide for more Information.