means A mathematical function that tells you the power to which a fixed number (the base) must be raised to produce a given number, turning multiplication into addition and division into subtraction.

from Coined in the early 17th century by the Scottish mathematician John Napier, who stitched together two Greek words: logos, meaning 'ratio' or 'reckoning,' and arithmos, meaning 'number.' So a logarithm is, quite literally, a 'ratio-number' — Napier's name for the clever bookkeeping of proportions that let weary astronomers and navigators trade grinding multiplication for gentle addition.