What is Android MultiDex?

Question

There are many posts about MultiDex. I have experienced, sometimes, errors solved including multiDexEnabled true in the defaultConfig section of my

Answer 1

It's as simple as this

A single .dex file can have 65,536 methods(references) so if the number of references exceeds 65,536, you go with multidex.

More Explanation!

An android application program is compiled into a .dex file which in turn zipped to a single .apk file.
DVM (Dalvik Virtual Machine) uses .dex file/files to execute bytecodes.

What causes the number of references to exceed 65,536 limits?
Methods written by you + Android Framework methods + Third party library(eg Volley,Retrofit, Facebook SDK etc) methods.
I have read "somewhere"
App Compat 24.2.1 contains 16.5k methods
Google Play Services GCM 9.6.1 contains 16.7k methods
So if you have created a simple Hello world application which has App Compat 24.2.1, you are already 1/4 way to cross the single dex methods limit