What does It's Accepted actually mean?

not much. Accepted means your tax return is now in the government's hands and has passed the initial inspection: prior year AGI is correct, dependents haven't already been claimed by someone else, SSN's valid and not used on another's return, and probably some other things.   this is not even close to saying the IRS will not find issues with your return.  for example, for 2019 returns more than a few taxpayers got their return accepted only to be notified by the IRS that Form 8962 (the Obamacare premium credit reporting form) was missing.  others got notified that amounts on their return did not match forms the IRS got from 3rd parties.