A shortened greeting/expression used to thank or acknowledge someone's efforts (short form of 'お疲れさま').
会議が終わって、同僚に『お疲れ』と言った。
After the meeting ended, I said 'otsukare' to my colleague.
遠くから来てくれて本当にお疲れ。ゆっくり休んでね。
Thanks for coming from far away — you must be tired. Get some rest.
仕事終わりに『お疲れ！飲みに行こう』と誘われた。
At the end of work someone said 'otsukare! let's go for a drink.'
As a noun, a polite form of 'tiredness' or 'fatigue', referring to physical or mental weariness.
最近よくお疲れがたまっているので、休暇を取るつもりだ。
I've been accumulating a lot of fatigue lately, so I plan to take a break.
長時間の残業で体にお疲れが出た。
My body showed signs of fatigue from long hours of overtime.
旅行の後は普段の疲れ以上にお疲れを感じた。
After the trip I felt more tired than usual.