n. 1. The act of indenting or state of being indented. [ 1913 Webster ]

2. A notch or recess, in the margin or border of anything; as, the indentations of a leaf, of the coast, etc. [ 1913 Webster ]

3. A recess or sharp depression in any surface. [ 1913 Webster ]

4. (Print.) (a) 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. (b) The measure of the distance; as, an indentation of one em, or of two ems. [ 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. [ 1913 Webster ]