You are a 疲れ (tired) 様 (honorific that kind of refers to whoever's being mentioned with this word). You say this to people after a day of hard work or after a good practice, etc. お疲れ様でした! I suppose the assumption here is that everyone worked until they were tired, so it was a good work, and then you thank them for it and mention how tired everyone is.
The reading comes from 疲れ and 様, combined together into one word.