Mathematical Bold Small K

𝐤 is the bold k in a mathematical alphabet; its equation determines what it names. In physics and applied math, a boldface k may stand for a vector, a quantity with direction and size. The bold form is a separate character, so changing it to plain k can erase a distinction the formula uses.

Text symbol

What 𝐤 means

Often, in physics and applied math, bold lowercase letters mark vectors.

A vector has direction as well as size; a scalar has size alone. The notation is conventional, and each equation defines what 𝐤 names. One documented turn came in 1886: Oliver Heaviside described adopting Clarendon bold type to distinguish vectors from scalars after Greek letters caused confusion and Fraktur (blackletter) proved hard to write and read.

Why is 𝐤 separate from plain k?

Its mathematical type style can carry meaning.

Unicode encoded mathematical letter styles as separate characters so plain text could preserve distinctions between symbols. 𝐤 is the bold math character itself; a formatting control applies visual emphasis to an ordinary k.

The precise outline can vary with the math font. Unicode’s chart glyph is an example, not a required design.

This mathematical alphabet is intended for math or technical notation; use ordinary text formatting to bold prose.

Changing 𝐤 to plain k can merge distinctions an equation sets apart.