F.R.E.D. stands for Field Remote Expeditionary Device, and is a supply robot on 8 wheels which can navigate almost any terrain. It was sent with Daniel Jackson, Jack O'Neill and his team to Abydos. (Stargate)
The M.A.L.P. was later sent instead because it is better-suited as a probe by comparison to FRED. The FRED also appears to have a 'follow mode', it is most likely sonar guided so it can move without having constant human control over it thereby freeing up man power and reducing travel time. (SG1: "Children of the Gods")
Sometimes the planet is considered hostile and not even the M.A.L.P, F.R.E.D, or SG-1 can go through so they have to launch a UAV instead to carry out the mission. (SG1: "Enigma")