In the United States there are two major classes of crimes: felony and misdemeanor. A felony is considered a more serious crime than a misdemeanor.
The penalties for a felony are steeper than those for a misdemeanor, i.e., more jail time, or even death. Plus, as noted above, the loss of certain rights (e.g., the right to vote) and privileges (e.g., being a police officer, or becoming an immigrant).
The person convicted of a felony is called felon.
It is interesting that the US immigration laws prohibit one from immigration only if he was convicted of a felony. He may have committed it and not been convicted, and thus be eligible for immigration.
For example, a woman may have been a prostitute in her country. While prostitution is a felony in many US states, if it was OK in her country, and thus she was not convicted for a felony there, she may be permitted to immigrate to the US even if she admits to having been a prostitute.