Hi Shigeki, Stressed out means a condition where someone is irritable and feeling tired. The word "out" is optional. We can also write: She seems stressed (adjective). It seems to me that the phrase "stress out" functions as an adjective too. Hope this helps. Cheers, Lance

"stressed out" is a shortened version of "stressed out their mind". An exaggeration saying that the person is so stressed they are now crazy.

Thank you for your answer. I think that I got it alomost.

I would say no. You could leave it off and it would mean the same thing. She seems stressed. Similar to "pissed off". She seems pissed off (as in being mad). (Only say this among friends however because it's kind of a crude word...pissed). You could also say She seems pissed. And leave off the "off" word in my sentence and it means the same, they really have no extra meaning. But most people add the word out to your sentence. She seems stressed out. And sentence is with a c not an s (on your second c). ;o)