A boson is a particle which behaves usually as a force-carrier. Each of the four fundamental forces (Strong Nuclear, Weak Nuclear, Electromagnetic, and Gravity) has one or more bosons (called gauge bosons) that transmit the respective forces. These gauge bosons are the quanta of the forces. Bosons, which have an integer spin, can occupy the same space unlike matter (feminons) which cannot. The Higgs Boson which is being searched for by the Large Hadron Collider is also a boson which gives particles mass; it does not belong with the four fundamental forces but is still a boson (it has an integer spin).
The graviton is the gauge boson for the gravitational force.
1: Pretty much the best poker hand you can get trumping all but a Straight Flush or a Royal Flush. The chance of obtaining such a hand with a 5 card deal is .024% (.00024) In games such as Texas Hold Em', it is possible for more than one person to share the same 4 pairs which in that case the unmatched card determines who wins the pot (if they are the same, pot is split).