What is "link to executable"?

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http://askubuntu.com – What is "link to executable" ? I'm trying to understand what "gcc" is. If I open Properties of it in Unity UI it says "link to executable". I googled it. Tried following commands link readlink ln I'm confused. What command I should use in order to: check whether file is link or not view where link points to change destination of a link (I need to repoint gcc to gcc 4.7 in my case) (HowTos)