A parent who has "physical custody" of a child has the right to provide day-to-day care for the child. The key aspect of physical custody in most child custody situations is that the child will live with the parent who has physical custody. Most modern custody arrangements give physical custody to one parent (called the "custodial" parent) and grant visitation rights and shared "legal custody" to the non-custodial parent. Typically, visitation rights give the non-custodial parent exclusive time with the child every other weekend, alternating major holidays, and a number of weeks during summer vacations.
In the past, true "joint physical custody" arrangements were more common, in which the child lived with each parent roughly half the time. Today, such arrangements are rare, and in order to lessen disruption of the child's routine, one parent is usually given primary physical custody of the child.
Example: Mother and Father have divorced, and share legal custody of Child, while Mother is given physical custody of Child. This usually means that Mother and Father share equally in making important decisions concerning Child's upbringing, but Child lives with Mother for the majority of the time. As in most cases where one parent is awarded physical custody, Father is given visitation rights as the non-custodial parent -- entitling him to exclusive time with Child every other weekend, on alternating major holidays, and for four consecutive weeks over Child's summer vacation.