What ℊ means
The surrounding formula gives ℊ its meaning. Math writers may use script g to distinguish one quantity or object from plain g, but the letterform alone does not tell you which one.
Lowercase g changed shape across Roman, Carolingian (a medieval writing style), Gothic and cursive hands: loops opened or closed, and some forms added curls or a stroke descending below the line. ℊ is a script-styled form of ordinary Latin g within that longer history, not a universal mathematical operation.
Technical in formulas; in running text, it reads as a stylized lowercase g.
The script face can mark a distinction; the formula tells you what ℊ denotes.
Don't confuse it with
1Questions people ask
1Why does ℊ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type ℊ
ℊ\210ACodes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.