What is the negative logarithm of the hydrogen ion concentration known as?
The logarithm of the hydrogen ion concentration in a solution, with the sign changed from positive to negative, is called the pH.
The term 'p' is used to denote the number that is the logarithm of something with the sign changed. We sometimes also talk about pOH (negative the log of the concentration of hydroxide ions).
The pH scale notionally goes from 1-14, although concentrated solutions of some strong acids can have a pH between 0 and 1. This scale, from 0-14 corresponds to concentrations of hydrogen ions from 10^0 (1)