means pH is a scale from 0 to 14 that measures how acidic or basic a solution is, with lower numbers meaning more acidic, 7 being neutral, and higher numbers more basic.

from Coined in the early 20th century by Danish chemist S. P. L. Sørensen while working on enzymes and brewing at the Carlsberg laboratory. The 'p' is the genuinely murky part: it's usually read as German 'Potenz' or French/Latin for 'power' (as in power of ten), while the 'H' is hydrogen — so pH is roughly the 'power of hydrogen,' a shorthand for the negative logarithm of the hydrogen-ion concentration. Sørensen himself was a bit casual about what the 'p' stood for, which is why chemists have been politely arguing about it ever since.