1. standard

Always create a new instance.

2. singleTop

This mode just only search instance on the top in the task stack. If instance already existed, then reused it. If not, then create a new instance.

3. singleTask

This mode will search task stack(each app had their own task stack). If instance existed, then used it and pop other upper instances in the task stack.

4. singleInstance

Instance is always at the top of the task stack and it is the only one in the whole task stacks(all apps task stacks).

https://stackoverflow.com/questions/3219726/android-singletask-or-singleinstance-launch-mode?noredirect=1&lq=1
https://stackoverflow.com/questions/23033550/difference-between-singletask-and-singleinstance
https://hit-alibaba.github.io/interview/Android/basic/Android-LaunchMode.html
http://ascii-iicsa.blogspot.tw/2011/07/activity-androidlaunchmode.html