As DeLanda explains it, an entity is never fully defined by its relations; it is always possible to detach an entity from one particular set of relations, and insert it instead in a different set of relations, with different other entities. For every entity has certain ‘properties’ that are not defined by the set of relations it finds itself in at a given moment; rather than being merely an empty signifier, the entity can take these properties with it, as it were, when it moves from one context (or one set of relations) to another. At the same time, an entity is never devoid of (some sort of) relations: the world is a plenum, indeed it is over-full, and solipsism or atomistic isolation is impossible.
Put differently, no entity can be absolutely isolated, because it is always involved in multiple relations of one sort or another, and these relations affect the entity, cause it to change. But this is not to say that the entity is entirely determined by these relations.