The difference between acupressure and acupuncture is that acupuncture makes use of needles to penetrate the skin, while acupressure simply uses a certain amount of force. Both modalities use the Meridian System.
It’s also worth noting that Acupressure and Reflexology both use pressure points. However, reflexology uses a different energy principle along with different point locations on the feet, hands and ears. It uses a different “map” from the one that acupressure employs.
The Meridian System is like a body map that specifies where the energy is flowing. Traditional Chinese Medicine practitioners believe that obstructions to these pathways are what causes a person to feel discomfort or get sick.
They performed acupuncture trials to identify points of the body that were somehow connected with a particular health problem. They found out that these points were organized and followed a unique pattern. Thus, the meridian map was developed.
There are 365 acupuncture points (or acupoints). Each point belongs to a specific meridian channel. There are 12 principal meridians and 8 smaller ones. Visit this resource page for an in-depth view of the Merdian System.