What does expose do?

It is a percent health attack.

In addition to normal damage from whoever attacked it, the enemy also takes damage = to 20% of his/her max health.

It makes Resistance win every time ;)

"weska24;d-121778" wrote:
Question is in the title^^^

As mentioned, when you hit someone who has Expose on them they take bonus damage (that's the white number) equal to 20% of their maximum health. It does significantly less % damage against raid bosses, though--otherwise it would be broke af.

Folks are mentioning Resistance because Resistance Trooper gets 55% turn meter whenever an enemy gains Expose. But, on top of that, Finn's leader ability, at its highest level, will give all Resistance 35% turn meter when someone who is Exposed takes damage (and reduce their cooldowns by 1). So with a good string of Exposes you can lock an opponent down and just take turns over and over while they sit there, because Poe's taunt will Expose and drop opponent turn meter.