Prevalence is how common something is — how much of it there is in a place, at a time, or among a group of people. It is a noun: it names the fact, not the thing itself.

Prevalence is how common something isprevalence是指一個東西有多常見 — how much of it there is in a place, at a time, or among a group of people也就是在一個地方、一個時間點，或一群人裡面，那個東西有多少。It is a noun這是個名詞: it names the fact, not the thing itself它指的是「有多常見」這個事實，不是那個東西本身。

Doctors and news writers use it a lot. They might talk about the prevalence of a sickness, meaning how many people have it now. That is not the same as how many new people catch it this week; that other number has a different name.

Doctors and news writers use it a lot醫生和新聞寫作者很常用這個字。They might talk about the prevalence of a sickness他們可能會講一種疾病的prevalence, meaning how many people have it now意思是現在有多少人得了這個病。That is not the same as how many new people catch it this week這跟這星期有多少新的人染上不一樣; that other number has a different name那個數字有別的名稱。

You can also talk about the prevalence of a habit or an idea, though that sounds rather formal. Everyday English often just says how common it is, or how widespread.

You can also talk about the prevalence of a habit or an idea你也可以講一種習慣或想法的prevalence, though that sounds rather formal不過聽起來相當正式。Everyday English often just says how common it is, or how widespread日常英文常常就直接說「how common it is」或「how widespread」。

The word does not tell you if the thing is good or bad — only how much of it is around.

The word does not tell you if the thing is good or bad這個字不會告訴你那個東西是好是壞 — only how much of it is around只會告訴你它有多少、有多普遍。