AdblockPlus.org is the website.
What it does – Lets you surf the web without those annoying and sometimes dangerous ads (blocks banner ads, popups, even video ads).
What it is – Available for your favorite browser (Chrome, IE, FireFox, etc), you click on the Install button on their website and it installs a small add-on software program to your browser. Simple as that.
Cost – FREE!
Result – Safer, happier web browsing!