Sharepoint 2013 is Packaged with 3 different Apps models to move in the direction of the Cloud based hosting for your Apps.
Each one of these types of deployment models possesses characteristics that make it ideal for different types. You can choose the type based on the requirement.
|SharePoint Hosted App|
|No Server Side Coding|
|Can be used for Light Weight Apps|
|Scope : Site Collection|
|Scope :Site or Tenancy Level|
|Deployed to Windows Azure|
|Can be used to build data driven apps from Win Azure Web sites and SQL db|
|Code hosted in Separate Domain but not in Sharepoint which can be even windows Azure|
|All advantages of all the features of Win Azure Platform or IISor even PHP/Linux Server|
Will drive into samples in the following posts