Cologarithm

In mathematics, the base-b cologarithm, sometimes shortened to colog, of a number is the base-b logarithm of the reciprocal of the number. It is equal to the negative base-b logarithm of the number.

$\operatorname {colog} _{b}\ x=\log _{b}\left({\frac {1}{x}}\right)=\log _{b}1-\log _{b}x=-\log _{b}x=\log _{1/b}x.\,$

In chemistry, a decimal cologarithm is indicated by the letter p (originally the Greek letter ρ).
For example, pK = – log₁₀ K and pH = – log₁₀ [H₃O⁺].

References

• Meriam Webster definition of cologarithm
• "Cologarithm." From MathWorld--A Wolfram Web Resource.