What ⟱ means
It points downward; notation supplies any narrower reading.
In mathematical writing, an arrow’s role comes from its formula or legend. ⟱ alone does not specify a particular operation.
It appears in a mathematical-symbol proposal
A January 2001 proposal to add math symbols lists the downwards quadruple arrow among candidates identified in a review of mathematical literature. By 2007, a proposal for mathematical and technical publishing treats ⟰ and ⟱ as an existing up/down pair. Its authors proposed left- and right-pointing counterparts after reviewing STIX, a font project for scientific and mathematical publishers, and noticing those directions were missing.
Don't confuse it with
4Questions people ask
1Why does ⟱ 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 ⟱
⟱\27F1Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.