Features represent areas of a specific past activity. They may be hearths, pits excavated by prehistoric peoples for storage or garbage dumps, house basins, walls, and so forth. Features were often formed in a short period of time, and become a snapshot of the past. What distinguishes a feature from another kind of artifact is that the feature itself is not portable, it can't be brought into the lab. Archaeologists can excavate a hearth and retrieve the material IN the hearth, but not the feature itself. That is recorded through the photographs, maps, soil samples, and so forth, that describe the pit or hearth.
Features are usually some sort of pit into the ground. People used pits in the ground in much the same was that we use root cellars to store perishable items. Storage pits would have been used until they became infested with rodents and insects, and then were often used to dump trash. Often the soil in a feature turns black from decayed organic matter, so that features show up as dark stains in the ground.
