Spotify introduced Spotify Connect for iOS devices a few months back, but now it has made the feature multi-platform by adding it to the Android app.
Spotify Connect allows users to stream music over Wi-Fi to select speakers. The system will only work with streaming content rather than local MP3s, and it will need a Premium account to work. At the moment, it will also only allow you to send music to a single device, but that could change in the future.
Spotify Connect isn't much different from what you can already do with most Bluetooth-enabled devices and a Bluetooth speaker system, but it does eliminate the hassle of pairing.
In addition, because Spotify Connect leverages Wi-Fi, it has a further range than what Bluetooth can provide, and it means your friends will be able to share their own playlists or music, as long as they have the Spotify app and your Wi-Fi password.
Unlike similar streaming functionality, such as Apple's AirPlay, once you've pressed the Spotify Connect button, your Android phone will be free to do whatever else you need to do. In other words, you can do things like answer phone calls without stopping the music.
To see what else Spotify Connect can do, check out the Spotify for Android app from Google Play.