The original meaning of "Gershayim" is to denote a note of cantillation in the reading of the Torah, taking the form of a doubled curved stroke printed above the accented letter.
The name is now often applied to a double apostrophe (״) used to denote acronyms. This is written between the second-last and last letters of the non-inflected form of the acronym[1], e.g. "report", singular: "דּוּ״חַ" (which stands for "דין וחשבון"); plural: "דּוּ״חוֹת"; or "squad commander", masculine: מ״כ (which stands for "מפקד כיתה"); feminine: "מַ״כִּית".
Gershayim are sometimes also used in the same typographical manner to indicate that the sequence of letters represents a number rather than a word. This is used in the case where a number is represented by two or more Hebrew numerals (e.g., 18 → י״ח).
In older texts it is sometimes used to denote the transliteration of a foreign word, and is placed between the last and the penultimate letter: this function corresponds to the use of italics.
Computer encoding
Since most keyboards do not have a gershayim key, often people will substitute a quotation mark.
