What does お疲れ様 Otsukaresama mean?

Otsukaresama tells someone you can see they have been working. It functions as a greeting, a farewell, a thank-you and a closing marker, and English has no single phrase that occupies that position.

The construction

疲れ (tsukare) is tiredness, from the verb to become tired. The honorific prefix and the elevated suffix on the end wrap it in politeness, producing something that treats the other person's fatigue as worthy of respect.

Stated flatly in English it sounds absurd: you must be exhausted, said on arrival. In use it is unremarkable, in the way that asking how are you is unremarkable despite nobody wanting the answer.

What it does

Passing a colleague in a corridor. Leaving at the end of the day, in both directions, from the person going and the people staying. Finishing a task together. Closing a call. Acknowledging that someone has come back from something difficult.

The register shifts with the form. There are shorter, more casual versions between equals and fuller ones upward, which is the same dial operating as with chan and kun.

Why English cannot copy it

English greetings ask about state: how are you, all right, how's it going. English farewells wish well: take care, have a good evening. Neither format acknowledges effort, and the phrases English has for that are reserved for occasions rather than repeated daily.

Good work sounds like an evaluation from a superior. Thanks for your hard work is stiff and reads as insincere when said twice in one day. The Japanese phrase is neither evaluative nor effortful, because its frequency has worn the meaning smooth.

What the frequency implies

That effort is the default assumption. The phrase treats it as given that the other person has been expending themselves, and greets that rather than greeting them.

Read alongside salaryman and karoshi, that is not purely a warm observation. A workplace vocabulary organised around mutual acknowledgement of exhaustion says something about how much exhaustion there is to acknowledge.