The term Tilt Shift refers to two types of lens movements to create two completely independent effects and shouldn’t be interchanged.
Tilting a lens adjusts the angle at which the plane of focus hits the film or sensor, thus increasing or reducing depth of field without changing the aperture size. This is especially useful for landscape photography where the aim is to get as much of the scene in focus as possible without introducing long shutter speeds or diffraction.
Large format photography has always had the ability to tilt as the lenses and film backs are always moved independently of each other, with a concertina bellows between them keeping the light out.
In 35mm photography it’s always necessitated a large and expensive lens to create these effects and so hasn’t been as accessible to the general user.
Shifting a lens is mostly used to correct perspective distortion in architectural photography. With a regular lens, when you tip a camera upwards to include as much of the building as you can, it appears to fall back away from the camera due to perspective. A shifted lens compensates for this. Again it is possible to do this on a large format camera with no special apparatus.
The problem I have is with people’s use of the terminology. The Internet seems to be awash with “Tilt shift” images, real or photoshopped, where the effect is actually only the result of a tilt.
Can we all just get it right now please?