Guild Wars 2

Exactly what does “disabled” mean in the trait description?

Hammer damage is increased by 25% when a foe is disabled. Reduces cooldown of hammer skills by 20%.

Knocked down?
Dazed?
Stunned?
Snared?
All of the above?

From my experience with using a Hammer, any of the control effects cause more damage output.

Control Daze Float Knockdown Launch
Pull Push Sink Stun

I don’t remember an increase in damage when someone had the conditions chilled, crippled or immobilized.

Some developer input would be nice. The description is annoyingly vague.

The description is not vague, your ability to understand it is lacking. Disables are all forms of control in this game stunbreaks remove, so your question has already been answered. Previously Merciless Hammer only worked on knocked down foes, they buffed it to include all forms of hard CC.

Stuns, Knockdowns, Knockbacks, even Daze, anything that disables your character will affect the skill. Roots, snares, chills, other conditions do not.