A pluot is a hybrid between a plum and an apricot, made, as you would assume, by the two "getting it on." You can taste both, but it definitely leans more plum. They are delicious.
Where can you get pluots? Heaven. If you are not dead however, I believe many grocery stores now carry them, though the local one may be sold out because I bought every single one they had. Early bird catches the pluot.
It is definitely my favorite hybrid fruit - followed closely by the pineapple, which I believe is a hybrid between apples and pine cones.