Mathematical Bold Script Small Z

It is a bold-script z; the formula defines what it stands for.

The heavier stroke and cursive z shape belong to an alphabet of mathematical styles such as bold, italic, and script (calligraphic handwriting). In a formula, style can distinguish one mathematical object from another; no single value is reserved for this lowercase z.

A 1998 proposal to Unicode, the character standard used across devices, called for full mathematical alphabets, expanding earlier isolated letterlike symbols. It argued that style can change a symbol’s mathematical meaning and preserve that distinction in plain text. Decorative use in ordinary text is an unintended side effect.

What does 𝔃 mean when sent?

Read the context first; this character has no fixed message.

If the conversation is about an equation, it names the z the writer assigned. In ordinary chat or a display name, it may be a decorative z; its letterform alone does not identify a particular number, quantity, or idea.

Should I use 𝔃 as a font style?

No; use ordinary z when plain-text matching matters.

𝔃 is a separate character, not a formatting command. Exact-text tools may not match it when someone searches for plain z, so write ordinary words and names with ordinary letters; use font styling when the typeface, rather than the character, should change.