A polite phrase used to thank or acknowledge someone's hard work; often used by a superior toward a subordinate (similar to “Good job” or “Thanks for your hard work”).
部長：今日の企画、よくやった。ご苦労様。
Manager: You did well on today's project. Thank you for your hard work.
掃除が終わったら、先輩に『今日はご苦労様でした』と言った。
When the cleaning was finished, I said to my senior, 'Thank you for your work today.'
上司が帰るときに、部下に向かって『ご苦労さま』と言ったが、場面によっては注意が必要だ。
When the boss left, he said 'gokurō-sama' to his staff, but you need to be careful with the tone depending on the situation.