What Is The Difference between pip, pip3 and pip3.6 Shipped with Anaconda3?

On Windows system, if you install Python3 via Anaconda. Under Anaconda root directory, there is a directory named Scripts, in which pip.exe, pip3.exe and pip3.6.exe all exist. When we want to install a package, a natural question arises, is there any difference if I use pip install PACKAGE or pip3 install PACKAGE?