Deportation is the process the US government begins to remove an alien from the United States. The process of removal begins by either the apprehension of the alien or by the filing of a notice to appear (NTA) and serving this NTA on the alien. The alien then must appear in court to face the immigration charges or they risk being ordered removed in their absence.
The NTA charges the alien either under section 212 proceedings or section 237 proceedings dependent on the status of the alien. Aliens charged under section 212 are present in the country without an inspection and are charged as inadmissible because they have committed an immigration violation or possibly a crime. Aliens charged under section 237 proceedings have been lawfully admitted into the country but have either committed a crime, fell out of status or committed some kind of immigration violation.
While in removal proceedings, the alien can apply for a number of forms of relief from removal. Cancellation of Removal, waivers, asylum, withholding of removal, convention against torture, VAWA and a number of others.