What is suspended mode in iOS?

Please take into account that the suspended mode is exclusively for iOS, i.e. iPhones and iPads. 

When an application has been working in the background for long periods of time, the system moves the application to this state automatically.

Please open the app, (foreground mode) as frequently as possible to avoid suspended mode. 

Active - the normal state of "in use" for an app. Background - the app is no longer on-screen but is still executing code. Suspended - the app is still resident in memory but is not executing code.