Beer head (also head or collar), is the frothy foam on top of beer which is produced by bubbles of gas, predominantly carbon dioxide, rising to the surface. The elements that produce the head are wort protein, yeast and hop residue. The carbon dioxide that forms the bubbles in the head is produced during fermentation. 

Tapper, A beer tap is a valve, specifically a tap, for controlling the release of beer. While other kinds of tap may be called faucet, valve or spigot, the use of tap for beer is almost universal. This may be because the word was originally coined for the wooden valve in traditional barrels. 

Why just the right amount of head is needed.

A good head helps release the aromas of the beer, especially the hops. Aroma is everything for enjoyment of a good brew. When enjoying a super-hoppy IPA, you should always use a glass that provides a large surface area for aromatics to rise from. It can also provide the a pleasant mouth feel.

Why do you pour beer at an angle?

Don't waste a great beer on a subpar glass. Tilt the glass 45 degrees. This will allow the beer to slide down the edge of the glass and prevent too much foam, also called head, from forming. Pour beer into the center of the glass.