What is a reverse complement?
DNA is double-stranded and the two strands run in opposite directions. The reverse complement of a sequence is the sequence of the opposite strand read 5′ to 3′: each base is replaced by its partner (A↔T, G↔C) and the result is reversed.
You need it whenever a feature lies on the minus strand, when designing reverse primers, or when comparing reads that map to the opposite strand.
Reverse vs complement vs reverse complement
The complement swaps bases without reversing; the reverse only reverses the order. Neither corresponds to a real strand read in the conventional direction, but both are useful in specific situations such as reading a sequence 3′ to 5′.
Ambiguity codes
IUPAC codes are complemented correctly: R (A/G) ↔ Y (C/T), K ↔ M, B ↔ V, D ↔ H, while S, W and N are their own complements.
Learn the method properly. Bioinformatics Foundations: Databases, file formats, alignment and the command line: the working toolkit of every bioinformatician. View the course.