concentration - the strength of a solution; number of molecules of a substance in a given volume (expressed as moles/cubic meter)

pH, pH scale - (chemistry) p(otential of) H(ydrogen); the logarithm of the reciprocal of hydrogen-ion concentration in gram atoms per liter; provides a measure on a scale from 0 to 14 of the acidity or alkalinity of a solution (where 7 is neutral and greater than 7 is acidic and less than 7 is basic)