from somewhere in cyberspace. OK, Wikipedia, you got me!
“The possibility of particles moving faster-than-light was first proposed by Robert Ehrilch and Arnold Sommerfeld, independently of each other. In the 1967 paper that coined the term,[3]Gerald Feinberg proposed that tachyonic particles could be quanta of a quantum field with imaginary mass. However, it was soon realized that excitations of such imaginary mass fieldsdo not under any circumstances propagate faster than light,[4] and instead the imaginary mass gives rise to an instability known as tachyon condensation.[1] Nevertheless, in modern physics the term "tachyon" often[1][5] refers to imaginary mass fields rather than to faster-than-light particles. Such fields have come to play a significant role in modern physics.
The term comes from the Greek: ταχύ, tachy, meaning "rapid". The complementary particle types are called luxons (which always move at the speed of light) and bradyons (which always move slower than light); both of these particle types are known to exist.”