Definition of ultrashort:
(adj) :
(technical or informal) Very short.
(adj) :
(finance) Having a very short term of investment, typically less than a year
(n) :
(finance) A bond with an extremely short term, typically less than a year
(adj) :
(sciences) Extremely short in duration, typically on the femtosecond scale
(adj) :
(physics, of a wave) Having a wavelength of between 1 and 10 metres