The Starcraft 2 team has changed the name of the protoss unit from Warp Ray to Void Ray. Karune also explains the differences of armor attributes between units.
Karune: At the moment, there is ‘light’ and ‘armored’ armor classes. Buildings also fall under the ‘armored’ armor class.
Attacks on the other hand are a bit more varied. There is bonus damage towards, ‘light, armored, biological, and massive.’ Knowing a unit’s damage bonuses will be very important in knowing what to use to counter certain units.
Biological units usually just mean they are not mechanical. Marines, Zerglings, and Zealots are biological. Non-biological units does not however mean they fall under the ‘armored’ class though and vice-versa.
For instance, Marauders are biological units but are armored. Nullifiers are mechanical units, but have light armor. Ultralisks, would fall under massive, biological, and armored. Though Battlecruisers would be massive, mechanical, and armored. These new categories also allow for many more soft counters in the game as well, giving slight bonuses to units against a certain type, but not have it as an overwhelming hard counter, where one unit wins the game easily.
Warp Rays, also known as Void Rays now, are especially good against high hit point units, as well as buildings.
Often, the strategy that sees the most Void Ray use is against Zerg, using these units to do surprise attacks or joint attacks. Many Protoss players who scout Zerg players going mass ground units, will fast tech to Void Rays in hopes to catch them without anti-air capabilities. Void Rays are also great to do an attack on their base while you have a diversionary force distracting them in another place. 2-3 Warp Rays could take out a Hatchery much faster than say that equivalent in resources of Mutalisks.