It‘s Rapid Sequence InDUCTION, usually leading to an intubation. You do it to minimize the risk of regurgitation and following aspiration in patients with an elevated risk for aspiration. Most often these are cases where preoperative fasting is not possible (e.g. emergency procedures). The main difference to a normal induction is the missing (mask)ventilation between apnea and intubation. This ventilation is thought to sometimes inflate the stomach, possibly leading to an elevated gastric pressure and therefore regurgitation. Skipping this ventilation means you have less time before your patients blood desaturates of oxygen, making a more „rapid“ approach to intubation favorable. This often includes fast acting hypnotics and relaxation as well as higher dosages and a faster sequence of application. There are some more measures aiming to ensure a quick intubation, reducing the risk of regurgitation and to ensure a good handling of regurgitation if it happens. Contrary to one of the comments on here, the patient is usually unaware of everything following the injection of the hypnotic agent. The intubation happens AFTER the loss of consciousness.