A triple agent is a spy who pretends to be a double agent for one side, while they are truthfully a double agent for the other side. ... It may also refer to a spy who works for three opposing sides, such that each side thinks the spy works for them alone.

What does double spy mean?

: a spy pretending to serve one government while actually serving another.

Why is Snape a triple agent?

One of the biggest twists in the entire Harry Potter franchise came when it was revealed that after years of torment and bullying, Severus Snape was a triple agent: he was working for Dumbledore while pretending to work for Voldemort and telling Voldemort he was pretending to work for Dumbledore.