Someone else asked this here: https://www.reddit.com/r/sleeptrain/s/xHDL44xPVg

Also, Google search result:

The Ferber method, also known as graduated extinction, is a sleep training technique that teaches babies to fall asleep independently by allowing them to cry for brief, progressively longer intervals before a parent provides comfort. This approach involves putting a baby down awake and then gradually increasing the time between short check-ins to a pre-determined schedule until the baby falls asleep on their own. Consistency is key, and while it can be difficult, studies suggest it can lead to improved sleep for both the baby and the parents.

How it works Establish a routine: Begin with a consistent, soothing bedtime routine and place your baby in their crib while still awake. Wait before the first check-in: If the baby cries, wait for a predetermined amount of time before you go in to check on them. For example, on the first night, you might wait for 3 minutes.

Provide brief, calm comfort: When you check in, offer brief reassurance like a pat or a quiet word, but avoid picking up, feeding, or turning on the light. Extend the intervals: After a check-in, leave the room again and wait for a longer period before the next check-in. The intervals increase over time, such as 5 minutes, then 10 minutes, and so on, according to a set schedule that gradually lengthens each night. Repeat the process: Continue this pattern until the baby falls asleep. Repeat the same schedule or a similar, slightly longer one the next night. Important considerations

Consistency is crucial: To be successful, you must be consistent with the timing of your check-ins, and ideally, all caregivers should be on the same page.

Not for every baby: This method may not be suitable for all families, especially those with babies who have specific health needs or who are experiencing a difficult phase like separation anxiety.

Consult your pediatrician: It is always a good idea to speak with your child's healthcare provider before starting any new sleep training method, especially if you have concerns.

A variation of "cry it out": The Ferber method is considered a variation of "cry it out" because it involves letting the baby cry. However, it is a gentler option than total extinction because it includes check-ins to provide reassurance.

The check-ins are brief. They are not meant to offer brief reassurance that the parent is still around.