Yes and no. In Android only one foreground app can run at a time, but there are background services too. They are usually important system services, but apps can add them too (they're needed to receive push notifications for example).
Go to Settings > Apps, swipe right to "Running". Then you can toggle between "Cached background processes" and "Running services". Killing a cached process (a previously active foreground app) doesn't really make a difference since it wasn't running anyway. Killing a service sometimes has an effect, but usually the service restarts automatically.
To permanently shut down a service, use the app Greenify
. It "hibernates" apps with background services but still lets you run the app when you need it. Keep in mind that you lose the functionality of that service (e.g. if you hibernate Facebook, you won't receive notifications when you receive Facebook messages).
But honestly, unless you installed some badly coded apps that use too many services, you probably don't need to.
Asus TF101: KatKiss 4.3.1 (#28)
Galaxy Nexus (GSM): 4.3 stock
Moto X (GSM Developer Edition): 4.4.2
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