Pleonasm
Redundancy of terms expressing the same idea — an error when accidental, a figure of emphasis when chosen.
Pleonasm juxtaposes words repeating the same information: "climb up," "plan ahead," "a tiny little dwarf." Accidental, it's a clumsiness every revision pass must hunt — redundancy dilutes the sentence and adds nothing.
Deliberate, it becomes a figure of emphasis: "I saw it, he said, saw it with my own eyes" doesn't describe better, it attests — pleonasm there works as an oath. The line between fault and figure rests on one criterion: does the effect read as chosen? In doubt, the reader will assume negligence; the benefit of the doubt never goes to the author.
Example
Fault: "free gift." Figure: "I heard it with my own ears."