A hanging indent is (1.) the reverse of a paragraph indent.
Indentation is the placement of text farther to the right or to the left in order to separate it from the rest of the lines. The typical paragraph indent is the first-line indent, which is used to indicate the beginning of a new paragraph. The hanging indent is the opposite to the paragraph indent and that is why it is also called "the reverse indent". In contrast to a paragraph indent, a 'hanging indent' refers to a paragraph that has all lines indented except the first one.