A residuary estate, in the law of wills, is any portion of the testator's estate that is not specifically devised to someone in the will, or any property that is part of such a specific devise that fails. It is also known as a residual estate or simply residue. Wikipedia

Any portion of the testator's estate that is not specifically devised to someone in the will, or any property that is part of such a specific devise that fails (for example, due to the death of the intended beneficiary preceding that of the testator). Wiktionary

Portion of the testator's estate that is not specifically devised to someone in the will. Wiktionary (translation)