Contiguous simply means touching or sharing a border, according to Merriam-Webster. When it comes to the United States, contiguous refers to all of the states that touch one another, without another country or a body of water coming between them. These are sometimes also referred to as the lower 48 states.
.apk extension stands for android package file. It is a file format used to distribute and install applications.It includes the programm codes ,assets ,resourses ,certificates and manifest file. .Dex extensions stands for Dalvix Executable files.
Apk is the android package. R.java (auto generated file) when compiled along with .class (java classes) generated .dex file but these files are not deployable. .dex files are then reprocessed along with manifest file, and other resources (mp3, video, image) and .apk file is generated. This file is deployable.