800W is its maximum thermal power rating..."RMS power" if you'd like, although that's really a faulty term.
Has nothing to do with how much power you can use and still get good results from the speaker. Especially at home, you can trade off a bigger enclosure for a flatter response and use less power to reach mechanical limits.
The misunderstanding that a thermal power rating is somehow how much power you need to send the sub is why you see so many posts here complaining about blowing subs, melting tinsel leads, etc...