Basicity is the measure of how basic a particular base is. pKb is a method which is used to determine the basicity of a compound. In understanding basicity we need to look firstly at what a base actually is and how the term base can be generally defined. However when discussing bases it is somewhat impossible to overlook the nature of acids as the two are intrinsically connected. Therefore as one would expect the site includes ample reference to acidity and shows how the acidity constant is related to basicity and how this constant can also be used to measure basicity.
There are many factors which effect basicity, but in brief the less stable the base is the stronger it is, and the more accessible the lone pair of electrons, the stronger the base will be. The following pages give further information on what affects the availability of the lone pair and the like.