两者是executory interest的两种类型。

executory interests指将来的利益；期待权益

指现由第三人拥有，但通过将来的遗赠或财产转让而在将来可获得的权益。它包括通过将来生效的不动产遗赠而获得的地产权，及通过财产转让或遗赠而获得的对动产的将来利益，但它不包括归复地产权〔reversion〕和剩余地产权〔remainder〕。此种利益得到衡平法和英国1535年《用益法》〔Statute of Uses〕的承认，但在早期普通法上则被认为无效。

An executory interest is a future interest in a transferee that must either divest the prior estate or spring out of the grantor to become possessory. Executory interests are non-vested interests and are subject to the Rules Against Perpetuities. There are two types of executory interests: shifting and springing.

shifting executory interest指转移期待权益。这种期待权益会终止与其同时创设的由第三人所享有的某种权益。

A third party interest in an estate in land created by the conditions of a grant wherein the grantor gives the land to a second party, but with the occurrence of a condition divesting the second party of the land in favor of the third party.

比如说，如果张三同意把自己的地产所有权给予李雷，但同时又同意如果李四从法学院毕业，就把自己的地产所有权给予李四，那么李四将会拥有转移期待权益，因为一旦李四从法学院毕业，将会剥夺李雷的地产所有权。

Joe gives land "to Mike, but if Harry graduates from law school, to Harry". Harry has an shifting executory interest because his graduation from law school divests Mike of ownership.

springing executory interest指源头期待权益。这种期待权益会终止地产让予人所遗留的地产权益。

An interest in an estate in land created by the conditions of a grant wherein the grantor cuts short the grantor's own interest in the property in favor of the grantee, contingent upon the occurrence of a specific condition.

比如说，如果张三同意一旦李四从法学院毕业，就把自己的地产所有权给予李四，那么李四将会拥有源头期待权益，因为一旦李四从法学院毕业，将会剥夺张三的地产所有权。

以下为相关双语示例，供参考：

Executory interest means a future interest in a third party that takes effect by cutting short some interest. It is divided into two types, shifting executory interest and springing executory interest, and includes any future interest that is not a remainder.

期待权益指通过“斩断”他人权益的方式享有的未来权益，包含转移期待权益和源头期待权益两种类型，但不包括任何不属于剩余地产权的未来权益。