The most specific term is seam carving. It’s a content-aware resizing/editing method that removes less-important areas of an image while preserving key subjects, so the left and right parts can be pulled closer together.

Common software names for this include:

• content-aware scaling / content aware
• liquid rescale / liquid resize

If done manually rather than automatically, related terms are compositing or sometimes stitching, depending on how the image is rebuilt. In practice, people often use “content-aware” features in editors, then do some manual touch-up if the result looks unnatural.