Widgets on sites

Widgets are a buzzword on the web.
What is a widget? Next, I will write only about widgets hosted on sites, I’m dropping the desktop, because While I myself do not use such widgets. I will try to give my definition, so:

A Web Widget is an interactive block hosted on a site, the code of which provides web service “A”, which hosts the content of service “A”.

So the main elements of this definition are:

1. interactive - i.e. allowing the site visitor to do something with this widget (for example, poke him and what else he would answer poking), although there are static ones, but I don’t associate them with the word widget, such can be called informers .
2. code - everything is clear without a code anywhere, nothing can be inserted without a code :)
3. Content - here is the beauty of the widget! Content around the head! If the first factor was not obligatory, and the second could not be avoided, then this factor directly depends on service “A”. Will there be a playlist on the widget or will it be a video, or maybe there will be a map! It is up to you! Reluctance to think? Then leave this part to users, and start to solve some really important problems :)

Another opinion about the widgets can be found on the blog Lady in search
This is the whole theory that has come to mind :) There will be practical work I will definitely write off :)