Advance Parole Travel Document is a temporary travel permission, which allows certain immigrant categories to travel back to the USA without applying for a visa. Advance Parole is intended for individuals with temporary protected status, U visas, adjustment of status applicants (according to Form I-485) and individuals with a grant of LIFE Act Family Unity Provisions benefits.
To apply for an Advance Parole you should submit Form I-131, Application for Travel Document. You must receive approval before travelling abroad, otherwise your application for an Advance Parole Document will be presumed abandoned.
Please note that there is no need to obtain Advance Parole if you travel directly between parts of the United States, only trips outside the US borders counts.