Sesshin, which means "to touch the essence" in Japanese, is Shinnyo-en's meditative training to help each individual nurture their buddha nature.
There are two types of sesshin in Shinnyo-en. One is "structured" (uso) sesshin, which consists of brief, face-to-face guidance between specially trained spiritual guides and members. This kind of training is given only at a Shinnyo-en temple and helps members to understand themselves in light of Buddhist concepts.
Then, that insight is to be applied and consciously taken further in daily life outside the temple through reflection on everyday circumstances. This outside effort is called "unstructured" (muso) sesshin. The Zen tradition also has a meditative method called sesshin. Although its aim is similar, its form is different in Shinnyo-en.