[OTSUKARE-SAMA]

It means 'Thank you for your hard work', so you can say it when you or your co-worker leave the work as 'GOOD BYE'. But people say it more often as 'Hi, what's up!'. It could be a casual greeting if you say 'OTSUKARE', or could be a formal greeting if you say 'OTSUKARE-SAMA-DESU'. But it's not super formal. Anyway, it's very useful word. I've been using it more than 5 million times in my life. You should remember it.