It means to take a position you don't necessarily hold, for the sake of argument, that opposes the majority or more popular position. Example: We're both against allowing big companies to pollute more. But I will play devil's advocate, and argue for reasons why we should let more pollution occur (even though I don't actually agree with it). So, it's a process for gaining other points of view, I guess. FYI: The term comes from the Catholic Church's canonization process. When someone argued that an individual should be made a saint, someone else would play "devil's advocate," arguing that the person should not become a saint.

to play 'the devil's advocate' is quite a tricky thing to get ones' head around, even for native english speakers! the devil's advocate is someone who points out the negative possibilities or consequences as a result of an action that is about to happen or has already happened. Often in conversation an individual will say "I hate to play the devil's advocate, but..." and will reveal a negative outcome that perhaps other people within the conversation may not have wanted to acknowledge. Example: / Person 1: I'm going to buy a one-way ticket overseas and never see these people again! Person 2: Why? Person 1: I don't want to face my problems anymore Person 2: I hate to be the devil's advocate, but... running from your problems will never solve them. Only postpone the inevitable / Do you see where the conversation went and why this phrase was used? It's usually an uncomfortable truth.