Baryon number Heavy particles interacting by the strong force. Protons and neutrons are examples of baryons. Lepton number Light particles, electrons and neutrinos, are leptons. Antiparticles annihilate with particles to produce pure energy, all mass disappears. Positrons are the antiparticle of electrons.
Antiparticles have negative lepton or baryon number, as appropriate.
Stellar balancing act dynamic equilibrium. A star spends most of its lifetime at a relatively constant size, temperature, luminosity, etc. while it fuses some fraction of its hydrogen into helium. During this time there is a balance between the forces inward and the forces outward. Forces inward due to gravity, without the forces acting outwards the star would collapse. Forces outward pressure Thermal pressure.