The Skill Unlock Pack is a purchase from the Guild Wars In-Game Store that gives complete access to all the skills of either Core, Nightfall, Factions, Prophecies, or Eye of the North.
The kit unlocks all skills from a specific campaign for use with PvP characters, Heroes, and tomes and also makes all non-elite skills available at any skill trainer of the right campaign.
Each kit costs 9.95 USD / 8.99 EUR / 5.99 GBP, and there are 5 in total.