An umbrella is the gizmo used to protect yourself from rain or sun. An umbrella can also be something that groups similar things, like an umbrella organization that protects and serves many smaller organizations.
An umbrella is that lightweight, collapsible cover that’s handy on a rainy day. People also use umbrellas to protect themselves from the sun. Since an umbrella covers people and things, umbrella is also a metaphor for something that brings unity. An umbrella agency brings together other smaller and related agencies. An umbrella term can be applied to many concepts. To bring things together in this way is to umbrella, as in “The merger umbrellas several companies.”