Definitions of umbrella:

• noun:   having the function of uniting a group of similar things

  Example: "The Democratic Party is an umbrella for many liberal groups"

• noun:   a formation of military planes maintained over ground operations or targets

  Example: "An air umbrella over England"

• noun:   a lightweight handheld collapsible canopy
• adjective:   covering or applying simultaneously to a number of similar items or elements or groups

  Example: "An umbrella organization"