Stop is an indirect magic spell in Final Fantasy VIII that stops a target from moving for the status's duration. The spell can also be be junctioned to boost stats, or to inflict or resist against the Stop status effect.
Stop is a rare spell that can only be drawn from a few enemies and draw points. Stop is more easily refined from Wizard Stones using the Guardian Force Diablos's ability Time Mag-RF. Wizard Stones can be refined to a broad range of spells, but can also be obtained from many enemies.
Stop applies the Stop status effect, which renders the target unable to act for around 13.3 seconds. Targets under Stop are also unable to avoid attacks. If the target was afflicted with any status effects prior to being stopped, the status effects are halted as well, meaning statuses like Poison and Regen won't damage or heal, and effects like Protect won't wear off.
Stop is cast using the Magic command, Selphie's Slot Limit Break, or Rinoa's Angel Wing. Casting Stop in battle increases compatibility with Doomtrain by 1 and with Siren by 0.6, but lowers compatibility with Cerberus by 0.8 and with Carbuncle by 0.2.
Stop provides minor boosts to stats, but more importantly, can be junctioned to either ST-Atk-J to repeatedly inflict Stop with physical attacks, or to ST-Def-J to provide immunity to Stop with 100 Stop spells. The latter is useful against enemies that can inflict the status effect, while the former is effectively the most useful immobilizing status effect to junction to ST-Atk-J, as it can allow the player to render an enemy unable to act permanently if the enemy is not immune to Stop.
Behind the scenes
The two field Stop draw points are in places related to stopped time. There is a Stop draw point at the Sorceress Memorial, the place where Esthar freezes sorceresses to suspend them indefinitely to prevent them from passing on their sorceress powers. There is also a Stop draw point in the Ultimecia Castle clock tower, whose clock has stopped.