If writing is illegible, you cannot read it, or you can read it only with great pain. The letters may be too small, too faint, too rushed, or piled on top of each other. A doctor's handwriting is the classic joke, but a wet stain, a bad photocopy, or a name scribbled in a hurry can all be illegible.

If writing is illegible如果字跡illegible you cannot read it你就看不懂 or you can read it only with great pain或是要很辛苦才看得懂 The letters may be too small, too faint, too rushed字母可能太小、太淡、寫得太潦草 or piled on top of each other或是疊在一起 A doctor's handwriting is the classic joke醫生的字跡是經典的笑話題材 but a wet stain, a bad photocopy, or a name scribbled in a hurry但一片水漬、一份印壞的影印本，或匆忙寫下的名字 can all be illegible也都可能illegible

Though actually, this word is only about the look of the marks. A page of simple English can be illegible; a page of hard English in clear print is not.

Though actually, this word is only about the look of the marks不過實際上，這個字只跟筆劃看起來的樣子有關 A page of simple English can be illegible一頁簡單的英文也可能illegible a page of hard English in clear print is not而一頁印刷清楚的難英文則不會

It is a normal, slightly formal adjective, used by teachers, clerks, and anyone who has to read other people's notes. It is not slang, and it is not about the law.

It is a normal, slightly formal adjective這是個普通、有點正式的形容詞 used by teachers, clerks, and anyone who has to read other people's notes老師、職員，還有任何得看別人筆記的人都會用 It is not slang這不是俚語 and it is not about the law也跟法律無關