The AirPort Express Base Station was part of Apple’s AirPort line of wireless products. Although its design was more compact and it had fewer features than the AirPort Extreme Base Station available at the time, the AirPort Express Base Station included the ability to receive streamed audio from a wirelessly connected computer that was running iTunes. The AirPort Express Base Station could play the streamed audio through speakers connected to its analog/digital audio output jack, a feature the AirPort Extreme lacked.
The original AirPort Express offered 802.11g wireless, contained an analog–optical audio mini-jack output, a USB port for remote printing, and one Ethernet port. The AirPort Express could only stream audio to a powered speaker or stereo system via iTunes—it could not stream video.
Source: Wikipedia
