Charity incubation refers to the act of an existing organisation supporting the creation of a new charity. This could involve providing things like training, advice, seed funding, connections, and operational support. It could also involve actively trying to work out what new types of new charities should be founded (e.g., which interventions it would be worth having a new charity working on) and then finding people to found those charities.
Two EA-aligned organisations that focus on charity incubation are Charity Entrepreneurship and the Longtermist Entrepreneurship Fellowship. Organisations that are not primarily focused on charity incubation but that engage in some charity incubation activities include GiveWell (via its incubation grants; GiveWell 2021).