1A polite phrase used to thank or acknowledge someone's hard work, often said by a superior to a subordinate — similar in meaning to 'good job' or 'thanks for your hard work'. Because it implicitly ranks the speaker above the listener, it should not be said to a superior.
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.'
上司が部下に向かって『ご苦労さま』とねぎらったが、逆に部下が上司に使うのは失礼にあたる。
The boss said 'gokurō-sama' to his staff to acknowledge their effort, but it would be rude for a subordinate to say it to their boss.