What is Ancillary Administration?

Legal Definition
Ancillary administration is "the administration of a decedent's estate in a state other than the one in which she lived, for the purpose of disposing of property she owned there." Another definition is the "administration of an estate's asset's in another state." This is often a necessary procedure in probate, because the decedent may own property in a state other than his domicile, which is subject to the law of the state in which it sits.

An ancillary administrator is the personal representative who handles the property in the other state under ancillary administration. Most major court systems will have forms and checklists for ancillary administrators to use.
-- Wikipedia
Legal Definition
When a decedent leaves property in a foreign state, (a state other than that of his domicile.) administration may be granted in such foreign state for the purpose of collecting the assets and paying the debts there, and bringing the residue into the general administration. This is called "ancillary" (auxiliary, subordinate) administration. Pisano v. Shanley Co.., 66 N. J. Law, 1, 48 Atl. 61S; In re Gable's Estate, 79 Iowa. 178, 44 N. W. 352. 9 L. R A. 218; Steele v. Insurance Co., supra
-- Black's Law Dictionary