It is a way of visualizing the carbon atoms of an open-chain organic molecule from an oblique angle and projecting that image on a 2-dimensional paper to appear like a carpenter’s sawhorse.
The two adjacent carbons of interest in a chain are drawn as a slant line, and its two groups form the hind and forelegs, with the third forming the head and the tail to resemble a horse from which the name draws an inspiration.

The Sawhorse projections are an important tool for drawing conformations in organic chemistry to understand the interatomic interactions that may affect molecular stability and reactivity.
Related Reading- Sawhorse Projections (an excerpt from the chapter- Drawing Organic Structures)
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