In the episode "Lifeline", the USS Voyager passed an itinerant class B pulsar with a rotation cycle that peaked for seventeen hours every 32 days. Starfleet used the opportunity to use the MIDAS array to amplify the signal of a communication through the pulsar so it could reach Voyager some 30,000 light years away, in the form of a compressed data stream. This allowed for them to send each other quick bursts of information (such as letters and tactical updates) every 32 days.
In real physics, pulsars are highly magnetized rotating neutron stars that emit a beam of electromagnetic radiation in the form of radio waves. While there is no such term as 'itinerant pulsar', there is a class of pulsar called rotation-powered pulsar, where the loss of rotational energy of the star powers the radiation. A rotation-powered pulsar is a rapidly rotating neutron star, whose electromagnetic radiation is observed in regularly spaced intervals, or pulses. It differs from other types of pulsars in that the source of power for the production of radiation is the loss of rotational energy (as opposed to other pulsars that derive their energy from the gravitational potential energy of accreted matter or the decay of an extremely strong magnetic field).
The actual observed periods of pulsars range from 1.4 ms to 8.5 s. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name. The rotation period and thus the interval between observed pulses are very regular. For some pulsars, the regularity of pulsation is as precise as an atomic clock.
The itinerant pulsar used to communicate with Voyager