“Dolly zoom” is a technique that was popularized by Alfred Hitchcock in his film Vertigo, after which it was commonly referred to as “Hitchcock zoom” and the “vertigo effect”. The basic idea is to photograph (or film) a subject while moving towards or away from it, and at the same time changing the focal length to keep the subject at the same size in each frame. French photographer Micaël Reynaud used this technique on a beach last year, snapping photos of a stone block at focal lengths ranging from 24mm when he was closest to it to 840mm when he was farthest away.
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Here’s a diagram created by Reddit user GeneralSarsby that shows the effective field of view of lenses of various focal lengths when used on a 1.6x crop factor sensor. You can also download the source svg if you want to edit or build upon it.

Image credit: Diagram by GeneralSarsby and used with permission