Strike is a Weapon type found exclusively in Fire Emblem: Radiant Dawn that exists outside of the weapon triangle. With the exception of Ashera's Judge, Strikes are exclusive to the Laguz. Most Strikes deal physical damage, with the notable exception of Judge and a White Dragon's White Breath, which deal magical damage.
Strikes are unique from other Weapon types in a number of ways: they cannot be unequipped or in any way removed from the user's inventory (such as trading or selling), they cannot be bought or found anywhere, and they have unlimited uses.
Also unique is that raising your weapon rank in Strikes will not allow you to use a wider variety of Strike weapons; rather, it will upgrade your current Strike weapon by adding 5 points of Might. In some cases (most notably dragons' breath), the weapon's Hit may also improve. It should be noted however, that a Strike's minimum weapon rank is A, while it's maximum rank is SS, meaning Strike weapons can only be upgraded twice at the most.