I'm relatively new to blender. When asking a question on this forum, I noticed one of my post got edited with (blender-internal) in the tag, could someone explain this?
From the Blender SE Help Site:
A tag is a word or phrase that describes the topic of the question. Tags are a means of connecting experts with questions they will be able to answer by sorting questions into specific, well-defined categories.
In your specific case, since your question dealt with texturing in the Blender Internal render engine (as opposed to the Cycles render engine), the tag was edited in by another user to help clarify this.
As @Timaroberts said in the comments, tags help to organize the site's content and to help other users easily find questions relating to the topic they are wondering about.