ParagraphIndent

ParagraphIndent is an option for Cell which specifies how far in printer's points to indent the first line of each paragraph of text.

A new paragraph is taken to start at the beginning of a cell, and after every explicit Return character in your text.

Negative settings for ParagraphIndent make the first line of each paragraph stick out to the left.

See The Mathematica Book: Section 2.10.10.

See also: AutoIndent, LineIndent, ParagraphSpacing.