An ester is a flavour resulting from the fermentation process. Some yeast produce fruity esters while others can be spicy, flowery, etc.
IBU stands for International Bitterness Unit and is a means for measuring the hop infused bitterness on a finished beer.
Lagering comes from the German language for storage and refers to allowing the beer to ferment, settle and mature over the course of several weeks or months. This is usually done at low temperatures which allow the yeast and various byproducts to drop out leaving behind a clear product.
Pitching is the act of adding yeast to wort. It is often considered the first time the liquid has ‘officially’ become beer.