Gullies: valleys or trenches believed to be created by the flowing of running water. Gullies on Earth often fill periodically with water when it rains, but the gullies on Mars no longer have flowing water.
Latitude: angular distance north or south from the planet's equator measured from 0 through 90 degrees. The equator is defined as 0 degrees and the poles are at 90 degree north and south. Because Mars is smaller than Earth, the distance between degrees is smaller on Mars compared to Earth.
Longitude: Angular distance on the planet's surface, measured east (or in some references west) from some prime meridian, from 0 to 360 degrees. Because Mars is smaller than Earth, the distance between degrees is smaller on Mars compared to Earth.
MDIM: Mars Digital Image Models from the Viking Orbiters. Orbiters imaged the entire surface of Mars at a resolution of 150 to 300 meters, and selected areas at 8 meters. This map is a mosaic of all of the images, and provides a nice overview of the entire planet. Large features are clearly visible, but the resolution is too poor to see smaller features like gullies or sedimentary layering.
MOC: Mars Orbiter Camera, which is onboard the Mars Global Surveyor. Both wide-angle images and narrow angle images were taken using this instrument. Wide-angle image resolutions range from ~2 to ~15 meters/pixel. The narrow-angle lens takes more detailed photos and can image features as small as 0.5 meters (1.7 feet) across. Images from MOC are higher resolution than MDIMs, but there is less coverage of the planet. So with MOC images, you can see smaller features much better. The HiRISE images will be able to image even smaller features, and HiRISE will be able to take color photos.
MOLA: Mars Orbiter Laser Altimeter, which is an instrument on the Mars Global Surveyor. This tool measured the height of martian surface features like mountains and depths of valleys, producing elevation maps precise to within about 30 centimeters (1 foot) in the vertical dimension. This is particularly useful for looking at the polar caps, seeing large canyons, impact craters and volcanoes.
TES: Thermal Emission Spectrometer, an instrument on the Mars Global Surveyor. This instrument studies the atmosphere and maps the mineral composition of the surface by analyzing infrared radiation, which scans for heat emitted from the surface of Mars. This instrument is used to look at the minerals on the surface of Mars and also to see if there are areas of high heat flow, like you would see in a hydrothermal region, such as Yellowstone National Park on Earth.
THEMIS: Thermal Emission Imaging System, a camera on Mars Odyssey that images Mars in the visible and infrared parts of the spectrum. This instrument is used to take photos of the planet and also to determine the distribution of minerals on the surface of Mars. The IR resolution of the instrument is 100 meters (328 feet) per pixel. Using visible imaging in five spectral bands, the experiment also takes 18-meter-resolution (59-foot) images.