The Hebrew words מֵרְכָא כְּפוּלָה translate into English as double mercha. This name is given since the mark that is used appears like two merchas.
Purpose
Dr. David Weisberg suggested[1] that the merkha kefula mark is found on words that refer to an aggadic tale. For instance, he claimed[1] that the merkha kefula of Zechariah 3:2 is meant to remind the reader of the aggadic legend that the high priest Joshua was literally thrown into a furnace (as recorded in the Talmud, b. Sanhedrin 93a).
Occurrences
The Merkha kefula mark appears in the following locations in the Torah: