A time stop was a process by which objects were stopped in time.
The Pandorica was equipped with all sorts of defences, including time stops. (TV: The Pandorica Opens)
Missy used her device to activate a time stop on all the aeroplanes in the air on Earth, allowing her to gain the attention of UNIT and Clara Oswald after the Twelfth Doctor went missing.
The time stop confused Clara at first, making her tell her students at Coal Hill School to turn on their phones and browse the internet for news of planes freezing. When they met, Clara convinced Missy to end the time stop. She called it a "parlour trick" and said she couldn't have done anything with them. (TV: The Magician's Apprentice)