We normally expect planets to be orbiting stars, and so far that is where we have found them; this makes them easier to find, space is very large and planets are very dim, so up until now they have been discovered by their effect on a much brighter star.
However, although we expect to find isolated planets in deep space, they are so dim none have been found previously.
Now an international group who were looking for small bodies called "brown dwarfs" by analysing data produced by the Pan-STARRS1 system, which takes a photograph of the whole sky every night, found an unsually cool object with a temperature of about 700 celsius.
Because it isn't near a star it is easy to study the spectra of the light it produces and to learn a lot about it. The planet seems to be about 6 times the mass of Jupiter, and probably only about 12 million years old which is part of the reason it is still warm, and hence detectable, it seems to have been created with a group of young stars which are moving at the same speed as it .
It also looks very similar to some planets of a similar size and age which have been imaged recently, so it may have been formed in a solar system and then kicked out by an interaction with another massive body, so it and other objects may be able to tell us more about the formation of gas giants like the jupier as it is far easier to study.
This has been long predicted. I'm glad that one has finally been found.
Ahh, energy :) We can live there...
The "planet" described is brown dwarf "6 times the mass of Jupiter". Brown dwarfs could be described as a "failed stars".