Fence Gates are an interactive block, similar to a door, that were first implemented in the Adventure Update (Beta 1.8) and were also implemented into Minecraft XBLA. Fence gates enable easy access to fenced-in areas without climbing over blocks or ladders to gain access. They can only be opened by right-clicking the gate and will always open away from a player.
Like fences, fence gates count as one and a half blocks tall for player and mob collisions, and one block tall for all other purposes. This means that when closed, a player cannot jump over a fence gate. When, open, however, they lose their hitbox entirely; this includes the posts in the model.