An STD is an illness that passes from one person to another during sex. AIDS, herpes, and several others are STDs. The letters stand for sexually transmitted disease.

An STDSTD is an illness that passes from one person to another during sex是一種在性行為過程中會從一個人傳給另一個人的疾病 AIDS, herpes, and several others are STDs像AIDS、皰疹，還有其他好幾種都是STD the letters stand for sexually transmitted disease這幾個字母代表的是sexually transmitted disease（性傳染病）

It is a plain medical term, and doctors, nurses, health teachers, and newspapers all use it. It is not rude and it is not slang — but it is a serious topic, so people usually say it carefully, and it is not a word that comes up in light conversation. You will see it on health posters, in clinics, and in school health classes.

It is a plain medical term這是一個很普通的醫學用語 and doctors, nurses, health teachers, and newspapers all use it醫生、護理師、健康教育老師、報紙都會用它 it is not rude and it is not slang它不是粗俗的字，也不是俚語 but it is a serious topic不過這是個嚴肅的話題 so people usually say it carefully所以大家講的時候通常會比較謹慎 and it is not a word that comes up in light conversation也不是輕鬆聊天時會提到的字 you will see it on health posters, in clinics, and in school health classes你會在衛教海報上、診所裡，還有學校健康課上看到這個字

It is far more common than the full three words; almost nobody says 'sexually transmitted disease' out loud. Say the letters: S-T-D. It takes a/an like a normal noun — 'an STD' — because the letter S is said 'ess', which starts with a vowel sound.

It is far more common than the full three words它比完整的那三個字常用得多 almost nobody says 'sexually transmitted disease' out loud幾乎沒有人會把'sexually transmitted disease'整句唸出來 say the letters唸的時候就唸字母 S-T-DS-T-D it takes a/an like a normal noun它跟一般名詞一樣要加a/an 'an STD'像'an STD' because the letter S is said 'ess', which starts with a vowel sound因為字母S唸作'ess'，是母音開頭

There is a newer term you should know: STI, sexually transmitted infection. Doctors increasingly prefer STI, because a person can carry an infection and pass it on while having no symptoms at all — so 'disease' is not quite right for those cases. Both terms are in use; STD is older and still very common, STI is the more careful modern one.

There is a newer term you should know還有一個比較新的說法你該知道 STI, sexually transmitted infection就是STI，sexually transmitted infection（性傳染感染） doctors increasingly prefer STI醫生越來越偏好用STI because a person can carry an infection and pass it on while having no symptoms at all因為有些人帶原並會傳染給別人，卻完全沒有症狀 so 'disease' is not quite right for those cases所以對這些情況來說，'disease'（疾病）這個詞不太準確 both terms are in use兩種說法現在都在用 STD is older and still very commonSTD比較舊，但還是很常用 STI is the more careful modern oneSTI則是比較講究的新說法

Worth knowing: in British English, STD also used to mean something completely unrelated — a long-distance phone call system (subscriber trunk dialling). Older British people may remember 'STD code' for a phone area code. That use has almost disappeared.

Worth knowing值得知道的是 in British English, STD also used to mean something completely unrelated在英式英文裡，STD以前還有一個完全不相關的意思 a long-distance phone call system就是一種長途電話系統 (subscriber trunk dialling)（subscriber trunk dialling，用戶長途直撥） older British people may remember 'STD code' for a phone area code年紀比較大的英國人可能還記得'STD code'指的是電話區碼 that use has almost disappeared這個用法現在幾乎已經消失了