A disruptor burst was a type of adjustable strength plasma discharge that could be fired from a Jem'Hadar plasma rifle or pistol. (DS9: "Tacking Into the Wind", "Change of Heart")
The disruptor bursts used on the Jem'Hadar weapons had three settings: a stun setting that caused unconsciousness, (DS9: "The Search, Part I") a lethal burst with anti-coagulants that were designed to slowly kill their enemies if the burst itself did not, (DS9: "The Ship", "Change of Heart") and a more powerful burst capable of vaporizing a humanoid size target. (DS9: "By Inferno's Light")
According to Star Trek: Deep Space Nine Technical Manual (p. 90), the Jem'Hadar pistol and rifle weapons were not plasma weapons, as the prop was identified in "Tacking Into the Wind", but instead that they fired phased polaron beams. According to the book, they have only a single setting, the lethal pulse. This would be inconsistent with the other settings seen used in "The Search, Part I" and "By Inferno's Light".