An antibottom is another name for the bottom antiquark.
An antibottom quark (or b-bar quark) is the antiparticle of a bottom quark. It has the same mass as a bottom quark but opposite electric charge and other quantum numbers. When a bottom quark meets an antibottom quark, they can annihilate each other and produce energy.
If the Standard Model is correct -- and the search for the Higgs was (basically) a test of the correctness of the Standard Model -- then a Higgs Boson of mass 126 GeV would decay into a bottom-antibottom quark pair about 56% of the time.
Probably the most famous such particle is the PROTON. Other subatomic particles with a positive charges include: positrons, up/charm/top quarks, antidown/antistrange/antibottom quarks, antimuons, and antitaus.