A blackbody is something that can absorb and emit radiation (kind of like heat or light). Infrared radiation is a type of radiation that we can't see, but we can feel as heat.
When something gets really hot, like a piece of metal, it starts to glow and emit infrared radiation. We call this "blackbody radiation."
Infrared radiative dissociation is when infrared radiation causes something to break apart, usually molecules. This happens because the energy from the radiation shakes the molecules so much that they can't stay together anymore.
For example, if you put a gas molecule into a chamber and then shine a lot of infrared radiation on it, eventually the molecule will break apart into smaller pieces. This can be useful in scientific research or industrial processes.
Overall, blackbody infrared radiative dissociation is a way to make molecules fall apart using heat that we can't see.