The act of indenting or state of being indented. [1913 Webster]
A notch or recess, in the margin or border of anything; as, the indentations of a leaf, of the coast, etc. [1913 Webster]
A recess or sharp depression in any surface. [1913 Webster]
The act of beginning a line or series of lines at a little distance within the flush line of the column or page, as in the common way of beginning the first line of a paragraph. [1913 Webster]

Hanging indentation, or Reverse indentation, indentation of all the lines of a paragraph except the first, which is a full line; also called a hanging indent.

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OXFORD DICTIONARY

Indentation, n.
1 the act or an instance of indenting; the process of being indented.
2 a cut or notch.
3 a zigzag.
4 a deep recess in a coastline etc.

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THESAURUS

Indentation

alveolation, alveolus, blaze, boss, bump, cleft, colophon, concavity, convexity, crena, cut, dactylogram, dactylograph, dent, depression, digging, dimple, dint, embossment, engraving, excavation, excrescence, feel, fingerprint, finish, footmark, footprint, footstep, fossil footprint, furrow, gash, gouge, grain, granular texture, hack, hollow, honeycomb, ichnite, ichnolite, impress, impression, imprint, incision, indent, indention, indenture, jag, jog, joggle, kerf, knub, lump, mark, mining, nap, nick, nock, notch, nub, pad, paw print, pawmark, pile, pimple, pit, pock, pockmark, print, protuberance, pug, pugmark, score, scotch, seal, shag, sigil, signet, stamp, step, structure, stud, sunken part, surface, surface texture, texture, thumbmark, thumbprint, vestige, wale, weave, woof

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ROGET THESAURUS

Indentation

Concavity

N concavity, depression, dip, hollow, hollowness, indentation, intaglio, cavity, dent, dint, dimple, follicle, pit, sinus, alveolus, lacuna, excavation, strip mine, trough, honeycomb, cup, basin, crater, punch bowl, cell, socket, valley, vale, dale, dell, dingle, combe, bottom, slade, strath, glade, grove, glen, cave, cavern, cove, grot, grotto, alcove, cul-de- sac, gully, arch, bay, excavator, sapper, miner, honeycomb (sponge), depressed, alveolate, calathiform, cup-shaped, dishing, favaginous, faveolate, favose, scyphiform, scyphose, concave, hollow, stove in, retiring, retreating, cavernous, porous, infundibul, infundibular, infundibuliform, funnel shaped, bell shaped, campaniform, capsular, vaulted, arched.

Notch

N notch, dent, nick, cut, indent, indentation, dimple, embrasure, battlement, machicolation, saw, tooth, crenelle, scallop, scollop, vandyke, depression, jag, notched, crenate, crenated, dentate, dentated, denticulate, denticulated, toothed, palmated, serrated.

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