If you mean autoflower bud, that's the stuff that flowers naturally after a certain period without altering the lighting cycle. Regular bud requires strict light/dark periods to begin flowering, but autoflower takes care of this on its own after a set number of weeks. The time from seed to harvest is generally shorter with autoflower strains, which is very convenient for indoor growers worried about time/stealth/etc. The downside is smaller plants with lower yields (generally).
You still need quality soil and lighting to grow autoflower plants.