Space travel was travel from one celestial body to another.
Development of the ability to travel through space was regarded as one of the first real steps species took in their development. The Time Lords developed space travel when "the universe was half its present size." (TV: Genesis of the Daleks)
For most species vacuum was an extremely hostile environment. Therefore, to travel to other world they needed to find a way of avoiding exposure to it. The most common way was building spacecraft. Mankind has learned it by mid-20th century. (TV: Day of the Moon); other species did it billions of years before. (TV: City of Death) Because of huge distances between stars and even greater ones between galaxies, faster-than-light travel was often necessary for a species to explore a significant portion of the Universe.
A faster but more difficult method was teleportation - direct transmission from one place to another, whether by technological (TV: The End of the World, Boom Town, The Time Monster) or supernatural (TV: The Brain of Morbius) means. The Kitlings were able to teleport by willpower. (TV: Survival)
Biological abilities Edit
Some species had a native ability to move through space, like star whales (TV: The Beast Below). Wirrn (TV: The Ark in Space), Rutan Hosts (PROSE: Shakedown) and the Eight Legs (TV: Planet of the Spiders) were also able to travel through space without any technology.
Humans and space travel Edit
Humanity's first sojourn into exploring space began in the mid-20th century with the launch of several satellites. (PROSE: Alien Bodies) In 1969, humans first landed on the Earth's only natural satellite, the Moon. (PROSE: Blue Moon) A second party, who believed themselves the first, landed in 1970. (COMIC: Moon Landing)
By the 1970s or 1980s, England had its own space programme. The XK-5 space freighter was tested there and took off from Devesham. It went missing and was assumed to have hit an asteroid. (TV: The Android Invasion)