Expertise

The Expertise attribute reflects a Ranger's skill when using certain skills. This is a primary attribute and may not be used by secondary rangers.

Guild Wars description

 * "For each rank of Expertise, the Energy cost of all of your attacks, Rituals, touch skills, and Rangers skills are decreased by 4%. Several skills, especially those related to Energy costs and skill recharge times, become more effective with higher Expertise."

General description
The Expertise attribute increases the spammability of ranger skills and certain other profession's skills by decreasing the cost. Expertise skills are used to enhance other skills and have an all round selection of skills.

Expertise reduces the energy cost for the following types of skills:
 * All Ranger skills
 * Attacks from any profession
 * Binding Rituals
 * Touch skills from any profession

No other types of skills are affected.