An archaeological site is a place (or group of physical sites) in which evidence of past activity is preserved (either prehistoric or historic or contemporary), and which has been, or may be, investigated using the discipline of archaeology and represents a part of the archaeological record. Sites may range from those with few or no remains visible above ground, to buildings and other structures still in use.

Beyond this, the definition and geographical extent of a 'site' can vary widely, depending on the period studied and the theoretical approach of the archaeologist.

It is almost invariably difficult to delimit a site. It is sometimes taken to indicate a settlement of some sort although the archaeologist must also define the limits of human activity around the settlement. Any episode of deposition such as a hoard or burial can form a site as well. Development-led archaeology undertaken as cultural resources management has the disadvantage (or the benefit) of having its sites defined by the limits of the intended development. Even in this case however, in describing and interpreting the site, the archaeologist will have to look outside the boundaries of the building site.

Traditionally, sites are distinguished by the presence of both artifacts and features. Common features include the remains of hearths and houses. Ecofacts, biological materials (such as bones, scales, and even feces) that are the result of human activity but are not deliberately modified, are also common at many archaeological sites. In the cases of the Palaeolithic and Mesolithic eras, a mere scatter of flint flakes will also constitute a site worthy of study. Different archaeologists may see an ancient town, and its nearby cemetery as being two different sites, or as being part of the same wider site. The precepts of landscape archaeology attempt to see each discrete unit of human activity in the context of the wider environment, further distorting the concept of the site as a demarcated area. Furthermore, geoarchaeologists or environmental archaeologists would also consider a sequence of natural geological or organic deposition, in the absence of human activity, to constitute a site worthy of study.