what in deference between node and node js?

I installed nodejs as per this documentation https://nodejs.org/en/download/package-manager/

then I checked i current version of Node js

:~/Downloads$ nodejs -v

v4.2.6

Still Older version of Nodejs

then I tried to install node via nvm as per this documentation https://askubuntu.com/questions/849270/how-can-i-install-a-tar-xz-file-from-nodejs-org

I got newest version of Node :~/Downloads$ node -v v7.9.0

But When I checked version of nodejs , got still old version of nodejs. I just confused about difference bewtween nodejs and node .

thanks in advance if any one help me to install latest version of Nodejs via ppa or by tar.xz file, I already tried each solution.

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