Any person who is in the process of adjustment of status may apply for an Advance Parole. The Advance Parole is a derivative right to a pending application for adjustment of status and this document allows smooth entry into the United States after a short trip abroad for people whose green card applications are pending with the USCIS.
It is important to note that a person who overstayed his status in the United States by 180 days but less than a year is inadmissible to the United States for a period of three years. Furthermore, a person who overstayed his status in the United States by one year or more is inadmissible to the United States for a period of ten years. This is commonly referred to as the three and ten bar of re-entry. Some people, who nevertheless traveled and are subject to the bar may be eligible for a Waiver of Inadmissibility, but you should not count on that.
Therefore, even if you were granted an Advance Parole by the USCIS you should consult a US Immigration Lawyer before traveling outside the United States.