A Space suit is a pressure suit to protect a human from the harsh extremes of Space. Due to the conditions on the Moon, people going outside will need protection in the form of space suits.
Space suits have to protect against vacuum and temperature changes, provide oxygen and remove carbon dioxide and provide communications. Spacesuits have to be easy to to get in an out of and move around in.
New spacesuit designs
Pressurised suits vs. skintight suits
All spacesuits used to date have been pressurized, i.e. filled with air. It can be difficult to move in these suits, and as such they are only pressurized to a third of normal pressure to allow easy movement. At this low pressure, someone could suffer nitrogen narcosis. This requires the person who will be executing the EVA to breath pure oxygen for a few hours to purge their body of nitrogen, or to "camp out" overnight in a low pressure atmosphere. This is time consuming and not practical if an emergency EVA were to be carried out. An alternative could be a skintight suit, like the MIT biosuit, however, these suits are difficult to enter and exit. A hybrid could be considered.
The Russian Orlan spacesuit is entered through the rear, with the backpack acting as a door, whereas the American EMU has various seals at the waist, the helmet, the gloves, the boots, etc. The russian system can be entered in only five minutes, and with one seal is considerably safer as well.
Suitport on Wikipedia The suitport may help prevent the problem of dust inside the habitat.
A large portion of this text is taken directly from the Marspedia article EVA_Suitmarsp. The revision history can be found there.