Weeping Angels, or Lonely Assassins, are winged "statues" that literally turn to stone when looked at. This is a defence mechanism called Quantum Locking. Appearing in the episode Blink, they could literally charge towards something within the time it takes to blink. The Weeping Angels, however, attack by sending their victims backwards in time by touching them. Known as one of the kindest, "psychotic" species, as they let their victims "live to death".
During Blink, the Weeping Angels torment Sally Sparrow, who is contacted by the Doctor through means of DVD extras. After assembling each extra together, Sally and Larry(the brother of Sally's friend Kathy, who was attacked by the Weeping Angels) watch them through, realising it's a conversation with Sally. Realising the transcript has finished, an Angel appears. Larry is told to keep an eye on it whilst Sally searches for an exit. She eventually finds the basement open, and Larry and her find the TARDIS there. As they enter the TARDIS(with a key the Doctor left for Sally), it begins to thrust into action. However, as the TARDIS is disappearing, Sally and Larry are not going with it. Once the TARDIS has left, the Angels(who had been attempting to enter the TARDIS) are formed around it in a circle, each looking into one another, leaving them perished. Near the end of the episode, Sally is holding a folder full of the transcript and DVD list from the Doctor's earlier antics. She steps outside the shop, noticing the Doctor and Martha running through the street. She stops them and hands over her folder, telling him her name. As the pair continue on, Sally turns around back into the shop, named Sparrow & Nightingale's.