"Breathe In. Breathe Out." refers to the basic process of respiration, where living organisms take in oxygen and expel carbon dioxide. This process is essential for survival, as oxygen is required for cellular functions and energy production. In humans, breathing is controlled by the diaphragm and intercostal muscles, which work together to expand and contract the lungs. In addition to its biological significance, the phrase is often used in mindfulness and relaxation practices. Techniques such as meditation and yoga emphasize controlled breathing to reduce stress and promote mental clarity. Focusing on the rhythm of breath can help individuals achieve a state of calm and awareness.