An "App"

A website "app" is any enhancement you want to perform on you site can be defined as a website app. Website apps can be built to include or manipulate content and images or offer better measurement of user behaviors.  In SiteApps, there are no limits to the amount of apps you can have per site.  We actually encourage experimentation and implementing similar apps to see what works best for you.

A "Deployed App" (or "deploy")

A "deployed app" (or "deploy") is an instance of an app that is actively running on your website. Each account type is authorized to implement a specific number of deploys. Free accounts are authorized for up to 10 "deploys" at once. If you'd like to add additional deploys to your site, please consider upgrading your account type.

Also, please note: SiteApps allows you to deploy more than one concurrent implementation of a single app. You can apply different parameters and URL restrictions to create different "versions" of the same basic app, executing it in different ways on different pages of your website (or to different audiences). In such cases, each "version" of the app running on your website counts as a single active app installation.