Blink

To blink was to rapidly close and open one's eyes. Noting the speed of the Weeping Angels, the Tenth Doctor warned "don't blink" to Sally Sparrow; as the Weeping Angels were quantum-locked, this brief period in which they were not observed provided an opportunity for them to move and claim their prey. (TV: Blink)

According to the Second Doctor, the normal range of human blinking was about once every ten or fifteen seconds. Observing that Tobias Vaughn blinked far less frequently than that, the Doctor found him to be inhuman. Indeed, Vaughn was actually a cyborg. (TV: The Invasion)

Jackson Lake, who believed himself to be the Doctor, noted that the Tenth Doctor did not blink when he spoke of Cybermen from the stars. In response, the Doctor asked Jackson if he remembered Sally and the Angels, only for Jackson to display no familiarity. (TV: The Next Doctor)

On Alfava Metraxis, the Eleventh Doctor warned Amy Pond against blinking as they faced the Weeping Angels. Amy found this task difficult over time, asking "Have you ever tried not blinking?" (TV: The Time of Angels) As the Doctor noted, however, even when one did not blink, the Weeping Angels could use the image captured in one's eyes to enter the mind. (TV: Flesh and Stone)

While aboard a prison ship resembling a hotel, Amy told Howie Spragg not to blink when faced by Weeping Angels which turned out to be an illusion. (TV: The God Complex)

Amy noted that she would only have to blink to be touched by a Weeping Angel and thus join Rory Williams in the past. Ultimately, however, she provided an opening by turning her back to the Angel. (TV: The Angels Take Manhattan)

On Trenzalore, the Eleventh Doctor warned Clara Oswald not to blink when they found Weeping Angels in the snow. (TV: The Time of the Doctor)

Other references
"On the blink" was a saying. (TV: Boom Town)