任意性分配信托，是指受托人有权决定是否向受益人分配信托受益或资产，受托人有权决定分配给谁、分多少、以及信托财产的收益累积的处置等权力。法院无法要求受托人，向某个受益人外面的债主支付信托利益来清偿他个人债务，但是可以要求受托人向受益人支付信托利益前，先“代扣”向债权人支付来清偿债务。这个时候，受托人就可以选择停止支付受益人信托利益。以达到“防挥霍”的功能。

“任意性分配信托”的英文表达为：discretionary trust。Wikipedia对其有如下释义：A discretionary trust, in the trust law of England, Australia, Canada and other common law jurisdictions, is a trust where the beneficiaries and/or their entitlements to the trust fund are not fixed, but are determined by the criteria set out in the trust instrument by the settlor. It is sometimes referred to as a family trust in Australia or New Zealand. Where the discretionary trust is a testamentary trust, it is common for the settlor (or testator) to leave a letter of wishes for the trustees to guide them as to the settlor's wishes in the exercise of their discretion. Letters of wishes are not legally binding documents.

Discretionary trusts can only arise as express trusts. It is not possible for a constructive trust or a resulting trust to arise as a discretionary trust.