the.com/indentation

means A gap or notch set in from the main line or edge — most familiarly, the blank space pushing text inward from a margin.

from From the verb 'indent,' which goes back to Latin 'dens' (tooth), via a medieval scribal practice: to 'indent' a document meant cutting its edge with jagged, tooth-like notches, often used to split a contract into two matching halves whose torn edges could later be fitted together to prove authenticity. The jagged-tooth sense gradually smoothed into the simpler meaning of a notch or cut, and by extension, the inward step at the start of a paragraph — the typographic 'tooth-mark' left in the margin.