The device isn't ruggedized to the point of, say, a Panasonic Toughpad, but it does have a high degree of both water and dust protection (IP67).
For example, the Galaxy S4 Active can be immersed in water up to a meter in depth for up to 30 minutes. IP, as noted above, stands for ingress protection, with the first number referring to the protection against solid objects and the second against liquids. The higher the number, the better the protection, as you might expect.
The Galaxy S4 Active has the highest value for protection against solids, 6, which means it is "Totally protected against dust." Its protection against liquids is the second highest level possible. 7 means it is "Protected against the effect of immersion between 15cm and 1m." A value of 8 would mean it would be "Protected against long periods of immersion under pressure."
Internally, the phone has the same 1.9GHz quad-core processor that many GS4s have (some get the Samsung Exynos 5 Octa eight-core processor) and 2,600mAh battery. The screen differs, though, as the Active has the same-sized screen, 5.0-inches, but it is an LCD screen, rather than the AMOLED display of the normal GS4.
Typical of these sorts of announcements, Samsung did not reveal the exact release date of the Active, saying only "summer," nor did it announce pricing.
It's the latest salvo from the GS4 cannon. In May, at Google I/O 2013, a "Nexified" stock Android GS4 was announced, which will go on sale later this month. Earlier this week Samsung announced the Galaxy S4 Mini, which shrinks the screen down to 4.3-inches.
Samsung, apparently, is not shy about leveraging its Galaxy S line for sales. Now, where is that Galaxy Note 3?