Time Lords are indistinguishable from Humans at a glance, but there are significant internal differences. The most obvious difference is that Time Lords have two hearts, but they also have telepathic abilities and extremely long lifespans. A Time Lord can easily expect to live for centuries, and they can further extend their lives via "regeneration", a process that physically renews the Time Lord's body, giving him or her a new appearance in the process. A Time Lord can typically regenerate twelve times, giving each a true life expectancy of millenia.
Time Lords have telepathic abilities, but their extent varies among individual Time Lords, and their capabilities are difficult to determine. They seldom engage in telepathic communication, but many are adept at shielding themselves against telepathic intrusion. Time Lords can apparently speak any language like a native without effort and share this ability with their traveling companions; this ability may be linked to their telepathy.
At an unspecified time in the distant past, the Time Lords discovered technology to create vehicles that could travel through time and space, essentially taking passengers to any location in the galaxy and any date in history. Their ability to move through space and time in this manner gave them immense power. They explored space and time, eventually becoming complacent, believing that they had learned everything there was to know and retiring to live esoteric lives of contemplation on Gallifrey. Their complacency and isolationism eventually left them vulnerable to repeated invasions by less advanced civilizations.