Advance parole, or reentry permit (as it is often called) is an advanced permission to reenter the U.S. It can be granted to a person whose adjustment of status application is pending and who must leave the U.S. for a "bona fide business or personal reason." This includes "travel for any reason which is not contrary to law or public policy." For persons seeking adjustment of status, advance parole will be granted for multiple entries and for the time period required to complete adjustment, in one-year increments.
Departure from the U.S. without advance permission to leave during pendency of adjustment application is considered abandonment. An exception exists for persons in valid H or L status and their dependents. Generally, if an L-1 or H-1 is not under exclusion, deportation and removal proceedings, he may travel while the adjustment of status application is pending without an advance parole. In this instance, the foreign national must be coming to the U.S. to resume his employment with the same employer the H-1/L-1 is authorized for, and be in possession of a valid H/L visa, and the original I-797 receipt.
Advance parole can be granted to a lawful permanent resident (LPR) who has applied for a duplicate I-551 or a visa waiver under INA Sec. 211(b), but who must depart for emergent reasons prior to the approval of his application. The USCIS District Director may also authorize (except in certain cases) the issuance of an advance parole for emergent humanitarian reasons. In addition, a U.S. consular officer may issue an advance parole to a person prior to his embarkation abroad.
Note, even if a person who was unlawfully present in the U.S. for 181 days/1 year prior to filing an adjustment of status is granted an advance parole, he will be subject to the 3/10 year bar from reentry back to the U.S.