Slow Breathing or Slower-than-normal-breathing involves taking long and slow abdominal breaths at a rate of about five to six per minute. In practice it means that both the length of the inhale and exhale will be around five to six seconds.
The idea of deliberate Slow Breathing is primarily to relax and calm down. It’s based on intentionally manipulating the Parasympathetic Nervous System (PNS), which is part of the Autonomic Nervous System (ANS).
The PNS typically tries to maintain, relax, or reduce the body’s activities and creates a “state of calm.” Think of regulating autonomous bodily functions such as blood pressure, breathing, blood flow, and heart rate.
A deliberately induced slow breathing rate then sort of “bypasses” the autonomy of the PNS and signals it that it (and thus the body) can enter the “rest-and-digest” state.
A well-known Breathwork modality that uses Slow Breathing as its core technique is Coherent Breathing.