This term refers to good things we do for other people. Such actions are done sincerely without any expectations for something in return. This last part is a key component of the concept of good works as intentions really determine everything (See Arcana Coelestia 6393). The Lord flows into good works, and the person doing them moves to a higher spiritual state.

Good works are connected to faith. A life of faith requires one to perform good works. Otherwise, a person is not actually living a life of religion. This is shown at the very beginning of Doctrine of Life:

“Religion is all about how we live, and the religious way to live is to do good.”

Of course, there is a bit more nuance to the matter (e.g. what's really good? who is it good for? over what time range?) but that’s what is all comes down to – doing good.

(Odkazy: Arcana Coelestia 3147 [2]; Divine Love and Wisdom 214-215)