Mohole, short for Mohorovičić discontinuity drilling hole

The word Moho stands for the phrase Mohorovičić discontinuity, the boundary between the crust and the mantle inside planet earth. Mohole is short for Moho hole, more precisely for a drilling hole all the way down through earth's crust to or beyond the Moho. Don and Florence Leet described the motivation for drilling that deep and pierce the Moho [1]:

Information on the Moho has been gathered in many parts of the world now. Lava for many if not all our volcanoes may be generated in the region near the Moho. The Moho probably holds the answers to several very important questions about our planet, and probably some we don't even know enough to ask yet. So great is our curiosity about it that there is actually a project for drilling a Mohole down to it for a firsthand sample of what is there.

Project Mohole was suggested in 1957 by Walter Munk, a member of the National Science Foundation (NSF) Earth Science Panel [2]. In a sense, this project was the inverse to the space program. Lack of funding, however, prevented its completion. No access to earth's mantle—then. But recent drilling projects are coming close to deliver Moho and mantle rocks [3].

Keywords: geophysics, drilling, earth's interior, earth's mantle

References
[1] L. Don and Florence Leet: Earthquake • Discoveries in Seismology. Dell Publishing Co., Inc, 750 Third Avenue, New York, N. Y. , 10017, USA, 1964; pages 83 and 84.
[2] Project Mohole, 1958-1966 [www.nationalacademies.org/history/mohole].
[3] R. Monastersky: Drilling shortcut penetrates Earth's mantle [findarticles.com/p/articles/mi_m1200/is_n8_v143/ai_13526575].