For a number x, the power to which a given base number must be raised in order to obtain x. Written log _bx. For example, log ₁₀1000=3 because 10³=1000 and log ₂16=4 because 2⁴=16.
From New Latin logarithmus, term coined by Scottish mathematician John Napier from Ancient Greek λόγος (lógos, "word, reckoning") and ἀριθμός (arithmós, "number"); compare rational number, from analogous Latin.