Mass. Gen. Laws ch. 209B § 1
As used in this chapter the following words, unless the context requires otherwise, shall have the following meanings:
"Contestant", a person who claims a legal right to custody or visitation with respect to a child;
"Custody determination", any court order, instruction or judgment, whether temporary or final, providing for the custody of or visitation rights with a child; it shall not be deemed to include any order or judgment concerning other child-related matters except to the extent such order of judgment contains a custody determination as above-stated;
"Custody proceeding", includes proceedings in which a custody determination is one of several issues presented for resolution, such as an action for divorce or separation, guardianship, and care and protection;
"Judgment" or "Custody judgment", a custody determination made in a custody proceeding, and includes an initial judgment and a modification judgment;
"Home state", the state in which the child immediately preceding the date of commencement of the custody proceeding resided with his parents, a parent, or a person acting as parent, for at least 6 consecutive months, and in the case of a child less than 6 months old the state in which the child lived from birth with any of the persons mentioned. Periods of temporary absence of any of the named persons are counted as part of the 6-month or other period;
"Initial judgment", the first custody determination concerning a particular child;
"Modification judgment", a custody determination which modifies or replaces a prior custody determination, whether made by the court which rendered the prior determination or by another court;
"Physical custody", actual possession and control of a child;
"Person acting as parent", a person other than a parent who has physical custody of a child and who has either been awarded custody of a child or claims a legal right to custody and includes an authorized social service agency exercising legal or physical custody of a child; and
"Parent", a biological, foster, or adoptive parent whose parental rights have not previously been terminated;
"State", any state, territory, or possession of the United States, the Commonwealth of Puerto Rico, and the District of Columbia.
Mass. Gen. Laws ch. 209B, § 1