The Mobile Analytic Laboratory Probe, or M.A.L.P., is a reconnaissance probe employed by Stargate Command and the Atlantis expedition to determine the conditions on the other side of an active wormhole before sending a team through, in order to make sure it's safe. This function was originally held by the F.R.E.D., but the M.A.L.P. was designed with far superior scanning and analytical equipment, allowing it to take a much more thorough reading of a planet.
The M.A.L.P. is a remote-controlled drone with a variety of instruments to determine the safety of travel through the Stargate. It can monitor atmospheric conditions to make sure humans can survive on the other side. It can also transmit audio and video to make sure the area is clear of any potential hostiles, as well as confirming the presence of a functioning Dial Home Device so the team can return. (SG1: "Entity", "Revisions")
The Tau'ri have used two different types of M.A.L.P.s. The first kind, the Mark I, is a small, tread-equipped vehicle with a short grappler arm. This version was used during the first mission to Abydos, as well as during the first three years after the formation of Stargate Command. The second kind, the Mark II, is much larger, has a longer grappler arm, and uses conventional wheels (three on each side) as opposed to treads. It is somewhat more unwieldy than the Mark I, but tougher. The Mark I was eventually phased out in favor of this model, though both were used at the same time during the transition. (SG1: "Urgo", "Entity", "The Sentinel", "Heroes, Part 1")
M.A.L.P.s of both types are employed in virtually every mission the SGC embarks on. They have often been disabled or destroyed when sent into hostile situations.
The Atlantis expedition employs the Mark II M.A.L.P. During their second mission, one of their M.A.L.P.s was lost when it was sent through a Spacegate. Lt. Colonel John Sheppard's team has also once used a "MALP on a stick" (a video camera duct-taped to a stick) to see what was on the other side of a time dilation field. (SGA: "Rising", "Epiphany")
While trying to find out why SG-10 didn't come through the Stargate from P3W-451 when they dialed in, the SGC sent a M.A.L.P. only to get what was a few seconds of video at a time instead of much more due to the time dilation effect of a black hole that was consuming the planet. Despite the time difference, the M.A.L.P.'s camera still responded to commands and they learned of the black hole by pointing the camera at the sky. The M.A.L.P. was abandoned on the planet as there was no way to retrieve it or SG-10. When later rescuing SG-10 from P3W-451, due to sabotaged plans, SG-1's anti-gravity shield device failed. As the wiring had burnt out, Major Samantha Carter used the wiring of the M.A.L.P. abandoned on the planet to temporarily fix the shield device, allowing them to effect an escape. Though the repairs quickly burned out, the wiring held long enough for them to escape the black hole and into hyperspace. The M.A.L.P. was destroyed when the stellar matter from Vorash's sun came through the Stargate. (SG1: "A Matter of Time", "A Matter of Honor", "The Cost of Honor")
The Goa'uld also designed a reconnaissance probe that was the their version of a M.A.L.P. The probes are sent to various planets to investigate whether or not it is worth a visit by the Goa'uld. The probe is equipped with plasma repeaters, a defense shield, and a subspace transmitter to alert its owners if it encounters hostiles. (SG1: "Heroes, Part 1")