A time stop is a magical field generated by Warlock magic that removes an area from the normal passage of time, effectively trapping an instance of time.
Description
A time stop is distinguished by an azure field placed over an area, the barrier preventing anything from leaving the area. Within a time stop, the outside world appears to progress slowly. The time stop spell has an additional mechanism that forces an organism to maintain their state of consciousness in order to keep them stable within the time stop. Should an organism change consciousness anyway, the mechanism would force them out of the time stop. When a time stop is about to resolve, lights (may) poke through the diminishing azure field.
Technology
The time stop was famously used by San D'Klass who created the Santa Claus or Father Christmas myth. He used the time stop power to enter human dwellings while the humans were asleep so that he could give them presents. The intention was to lessen human greed.
The time stop is traditionally maintained by at least five Warlocks, providing an average duration of 1 hour 30 minutes. Foaly mechanized the process by inventing emitters that would manage the upkeep instead, Warlocks would then need to channel their magic into the batteries of an emitter. The technology had vastly increased the efficiency of the time stop, allowing for up to 8 hours duration.
Exploits
In Artemis Fowl, Fowl Manor had been trapped within a time stop by the LEP. Artemis had studied about San D'Klass within the Book, and theorized that a change in consciousness could create an exit from the time stop. He experimented this with his mother, giving her narcotics to induce sleep, and observing that she had disappeared. He later secretly administered the same drugs into glasses of champagne that he drank along with Butler and Juliet.
In The Last Guardian, Foaly places goblins attacking his house in a time stop, making them feel 5 years in the space of 5 seconds. This implies that time stop tech has advanced considerably since the first book.
Film

- "It's a kind of temporal vacuum that they create so that they can operate unseen by human eyes. I read about it in Dad's journal."
"It's formidable."
"Einstein and Hawking were right. Time is bending all over. Anything could happen now. Anything is possible." - ―Artemis Fowl Jr. to Domovoi Butler[src]
In the Artemis Fowl film, the Time-Stop is known as a "time freeze." Any use of a time freeze requires the authorization of the executors. A time freeze was first put in place when a troll escaped to the surface and crashed a wedding party. The time freeze allowed the forces of LEPRecon to go in and neutralize the troll, then reset everything and mind wipe the humans there so that they would not be aware that anything odd had happened.
Later, when Artemis Fowl Jr. captured Holly Shot and tried to ransom her for the Aculos, Commander Root ordered a time freeze over Fowl Manor. She described it as being "exterior only," that she needed the young Artemis alive so that she could talk to him. She then sent in her forces, however, Artemis Jr. and his bodyguard Domovoi Butler held their own against them, then Domovoi shot the capsule which was being used to create the time freeze. With this, the time freeze became unstable. Foaly, the centaur genius in charge of tech, managed to hold it for a time, but it eventually it collapsed and the LEPRecon forces had to withdraw, lest they got sucked into a time bend.