Photogrammetry is the technique whose purpose is to study and define precisely the shape, dimensions and position in space of any object, using essentially measurements made on one or several photographs of that object.
A more updated definition of the American Society of Photogrammetry and Remote Sensing (ASPRS): "is the art, science and technology for obtaining reliable measurements of physical objects and their environment, through recording, measuring and interpreting images and patterns of radiant electromagnetic energy and other phenomena. "
The word photogrammetry derives from the word "frame" (from "phos", "photós", light, and "gramma", tracing, drawing), as something ready, available (a photo), and "metron", to measure.
So it turns out that the concept of photogrammetry is: "measure on photos". If we work with a photo we can obtain information in the first instance of the geometry of the object, that is, two-dimensional information. If we work with two photos, in the common zone to these (area of overlap), we can have stereoscopic vision; or in other words, three-dimensional information.
Basically, it is a 3D coordinate measurement technique, also called motion capture, that uses photographs or other remote sensing systems together with topographic landmarks on the ground, as a fundamental means of measurement.