Post-hypnotic suggestions are verbal suggestions I give you while you are “in trance”. These suggestions are designed to take effect after you are out of trance.
Post-hypnotic suggestions fix in place in your subconscious mind the idea that when you encounter a specific cue after you emerge from hypnosis, you will experience something naturally and uncritically, or automatically do something that is beneficial for you. The “post-hypnotic cue” or “trigger” will be something relevant to your issue.
It could be a neutral cue such as being touched on the arm, or seeing the color “red”, or a formerly negative cue such as being yelled at, or being in your motor vehicle in traffic, or a positive opportunity to make a good choice, such as standing in front of your refrigerator.