Contexts are single events or actions that leave discreet, detectable traces in the archaeological sequence or stratigraphy. They can be deposits (such as the back-fill of a ditch), structures (such as walls), or "zero thickness surfaciques," better known as "cuts." Cuts represent actions that remove other solid contexts such as fills, deposits, and walls. An example would be a ditch "cut" through earlier deposits. Stratigraphic relationships are the relationships created between contexts in time, representing the chronological order they were created. One example would be a ditch and the back-fill of said ditch. The temporal relationship of "the fill" context to the ditch "cut" context is such that "the fill" occurred later in the sequence; you have to dig a ditch before you can back-fill it. A relationship that is later in the sequence is sometimes referred to as "higher" in the sequence, and a relationship that is earlier, "lower," though this does not refer necessarily to the physical location of the context. It is more useful to think of "higher" as it relates to the context's position in a Harris matrix, a two-dimensional representation of a site's formation in space and time.
The principle of original horizontality states that any archaeological layer deposited in an unconsolidated form will tend towards a horizontal disposition. Strata which are found with tilted surfaces were so originally deposited, or lie in conformity with the contours of a pre-existing basin of deposition. The principle of lateral continuity states that any archaeological deposit, as originally laid down, will be bounded by the edge of the basin of deposition, or will thin down to a feather edge. Therefore, if any edge of the deposit is exposed in a vertical plane view, a part of its original extent must have been removed by excavation or erosion: its continuity must be sought, or its absence explained.
The principle of stratigraphic succession states that any given unit of archaeological stratification takes its place in the stratigraphic sequence of a site from its position between the undermost of all units which lie above it and the uppermost of all those units which lie below it and with which it has a physical contact, all other superpositional relationships being regarded as redundant.