Definition of "antiparallel"

(mathematics) (of vectors) Parallel but in opposite directions.

1. (biochemistry) Describing the orientations of the two strands of DNA.  examples

2. (biochemistry) Describing two beta strands comprising a protein's secondary structure that are aligned and hydrogen bonded but where the vectors describing the amino- and carboxy-terminal ends of each strand are oriented 180° relative to one another.  examples

(geometry) A line that forms equal angles with two other lines, but in opposite directions.  examples