WiFi Pineapples are small devices that work in much the same way as a standard WiFi router, but they are much more powerful. The ‘pineapple’ in the name comes from the fact that they have a cluster of WiFi antennas, rather than the single one you see on standard routers.
They are optimized to be able to launch large-scale WiFi attacks over great distances, and as a result are a powerful tool for hackers. Or, in fact, for anyone else. Learn more about WiFi Pineapple attack.