A spermatozoon is a single male sex cell — the tiny cell with a head and a long tail that swims to meet the egg. It means the same thing as 'sperm', but it is the formal, scientific word: you meet it in biology textbooks, medical writing and lab reports, while in ordinary talk people just say 'sperm' or 'a sperm cell'. The word is tricky in two ways. First the plural: it is 'spermatozoa', not 'spermatozoons' — the ending follows Greek, like phenomenon/phenomena. Second the sound: it has five syllables, sper-ma-to-ZO-on, with the stress near the end, and the final 'zo-on' is two separate sounds, not 'zoon' rhyming with 'moon'. It is a perfectly polite word — no embarrassment attached, which is part of why doctors use it — but because it is so technical, using it in ordinary conversation sounds oddly stiff, a bit like saying 'sodium chloride' when you mean salt.

精子（正式的醫學／生物學用語；日常口語說 sperm）