A hybrid mobile app is an web application built with web technologies (HTML, JavaScript, CSS) that is then "wrapped" in native device code to extend the functionality and availability of the app.
A hybrid mobile app is an web application built with web technologies (HTML, JavaScript, CSS) that is then "wrapped" in native device code to extend the functionality and availability of the app. This shell of native code allows the developer to bridge the gap between JavaScript and native functionality, allowing your web application to access device features (like the Contact list, Camera, accelerometer, etc.) that otherwise would not be possible. Wrapping your code in native code has the added benefit of greatly increasing your app's availability and marketability, since now your web app can be submitted to various app stores.
Many different projects exist for creating native apps, including Apache Cordova (formally known as PhoneGap), Titanium SDK, and Sencha Touch.