"Alignment" and "Justification" are slightly different things. Alignment refers to the point at which the text is "anchored", and can normally be set to be the left margin, the centre point of the line, or the right margin. Justification refers to whether or not additional space is inserted to make the margins "line up".
The two concepts are certainly very closely related.
Currently proofreading The Poison Belt, by Sir Arthur Conan Doyle.