It is a Reserve Feat from Complete Mage. Basically reserve feats give a spellcaster a relatively minor supernatural ability that they can use all day, the strength of which is based on how powerful of a spell they have prepared (or in the case of spontaneous casters, able to cast) of the right type.
For instance, Firey Burst creates a little 5' burst of fire that deals 1d6 fire damage per level of the highest level [fire] spell you have currently prepared. So a 5th level wizard with this feat, rather than just firing his one 5d6 fireball and being done, he could pop off many 3d6 Firey Bursts over the course of the day.
Additionally, the feats give +1 caster level to a certain type of spell as a side benefit. So that level 5 wizard example I mentioned would actually fire a 6d6 fireball when he cast it.
These are generally most powerful at low levels due to their short range and relatively low damage. At higher levels there are only a few that are really worth it. (Minor Shapeshift for lots of temporary HP being one example)