From the Wikipedia definition of "Meteor Burst Communications":
Meteor burst communications, or MBC for short, is a radio propagation mode that exploits the ionized trails of meteors during atmospheric entry to establish brief communications paths between radio stations up to 2200 kilometers (1400 miles) apart. It is also referred to as meteor scatter communications in some documents.
As the earth moves along its orbital path, tens of thousands of particles known as meteors enter the upper atmosphere. When these meteors enter the atmosphere and begin to burn up, they create a trail of ionized particles that can persist for up to several seconds. The ionization trails can be very dense, and used to reflect radio waves. The frequencies that can be reflected by any particular ion trail are determined by the intensity of the ionization created by the meteor, often a function of the initial size of the particle, and is generally between 20 MHz and 500 MHz.
The distance over which communications can be established is determined by the altitude at which the ionization is created, the location over the surface of the earth where the meteor is falling, the angle of entry into the atmosphere, and the relative locations of the stations attempting to establish communications. Because these ionization trails only exist for fractions of a second to as long as a few seconds in duration, they create only brief windows of opportunity for communications.
A nice read for anyone interested on radio communications. The known origins go back to 1929 when a Japanese individual, Hantaro Nagaoka, reported the interaction between meteors and radio waves propagation. Later in 1931, it was noticed that long distance propagation occurred at times of major meteor showers for a short time.