Jupiter is not really an actual failed star although it's called a failed star.
The reason that Jupiter is called a failed star is because Jupiter is made of the same elements (hydrogen and helium) as the Sun is.
However Jupiter is not massive enough to have the internal pressure and temperature necessary to cause hydrogen to fuse to helium, the energy source that powers the sun and most other stars.
So while Jupiter is made up of similar things as stars are the Jupiter is not really a star or really a failed star.
It's just called a failed star because of the similarities it has to stars.
Jupiter is not really a failed anything and was created to be what it is.
Jupiter is a planet and not a star.
The Planet Jupiter is the fifth planet from the Sun and is the largest planet in the Solar System.
Planet Jupiter is a gas giant with a mass one thousandth that of the Sun, but two and a half times that of all the other planets in the Solar System combined.