Wiktionary
gershayim
n. (context rare English) The Hebrew character ״, used to indicate acronyms and other multi-letter abbreviations.
Wikipedia
Gershayim (trope)
Gershayim (Hebrew גֵּרְשַׁ֞יִם, with variant English spellings) is a cantillation mark that is found in the Torah, Haftarah, and other books of the Hebrew Bible.
The Hebrew word גֵּרְשַׁ֞יִם translates into English as double geresh.