The Disruptor missile is an invention of the pirate faction; the Yaki. The missile uses enhanced ion particles to disrupt the electronics and engines of the vessel it hits, leaving the hull and other systems intact.
An extremely useful missile for killing M5s and M4s, the Disruptor missile is a rare drop from some NPC ships. It outspeeds most fighters and is very maneuverable, making it highly prized onboard frigates and slow battleships unable to chase down smaller craft. Good range makes it useful in many circumstances.
Note that this missile can not be bought anywhere in the game, but corporation quests will often ask you to deliver 10 or 20 of them. So if you see them dropped anywhere, it may be wise to collect them so you can later deliver them for one of the corporation quests.
In X3: Reunion, the Disruptor Missile played an important role in the plot, disabling ships and allowing the Yaki to capture them. In Terran Conflict and Albion Prelude, the missile simply damages other ships, and does not disable them.