Rogue Stars, not to be confused with Star Wars - Rogue One films are stars that don`t conform to the voyage of a star such as our own, the Sun. There are two main types of Rogue Stars, there might be others which will be added in due course.
One type of stars are Rogue Stars that either free the confines of the galaxy that they were once part of, these are also known as Intergalactic stars. There`s nothing horrible about these. The star HE 0437-5439 is on its way out of the milky way galaxy at a speed of three times the orbital speed of the Sun round the Galactic Centre. HE 0437 is not expected to hit our Sun but it is an example of a Rogue Star, one that we know exists. Once it leaves our galaxy, it will be a true Rogue Star.
The other type of Rogue Stars are one that move at a different speed and path to everyone else. The best example is the hypothetical brown dwarf star, Nemesis. The theory behind Nemesis is that every 26 million years there is a mass extinction which would coinicide with Nemesis coming closest to the Oort Cloud. When Nemesis gets close, it can send a comet in wards and hit Earth. Nemesis is a brown dwarf and so as it is dark, it is not easy to be picked up which is why its not yet been proven to exist.