[1] It is usually a part of the Cultural Resources Management (CRM) methodology and a popular form of rapid archaeological survey in the United States of America and Canada.
It designates a series of (c. 0.50 m or less) test holes, usually dug out by a shovel (hence the name) in order to determine whether the soil contains any cultural remains that are not visible on the surface.
STPs will often be laid out over the project area in a grid-like fashion or in a consistently spaced line, creating a fairly systematic survey.
Typically this ranges from 30 cm to 1.0 m. A second factor is mechanical, in that excavation is limited by the tools and techniques used (i.e., shovel versus trowel).
STP can be combined with other techniques and tools (augers, corers) to extend the maximum depth of effective testing beyond 1.5 m.