double bubble

Short definition from Wiktionary

Noun

1. 1
   The presence of two air-filled bubbles in the abdomen, often indicating various pathological conditions.
2. 2
   A fuselage formed from two conjoined hulls.
3. 3
   Overtime paid at twice the normal rate.
4. 4
   A certain meeting of spherical surfaces, relevant to the double bubble conjecture.