(1):

(n.) The act of indenting or state of being indented.

(2):

(n.) The measure of the distance; as, an indentation of one em, or of two ems.

(3):

(n.) 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.

(4):

(n.) A notch or recess, in the margin or border of anything; as, the indentations of a leaf, of the coast, etc.

(5):

(n.) A recess or sharp depression in any surface.