Inhalation is the act of breathing in, pulling air into your lungs. Right now, as you read this, you're inhaling and exhaling without even thinking about it: your chest expands as air rushes in through your nose or mouth, travels down your windpipe, and fills your lungs with oxygen that your body needs to survive.

Usually inhalation happens automatically, but you can control it too. Before swimming underwater, you take a deep inhalation to fill your lungs with air. When you smell cookies baking, you might take a deeper inhalation to enjoy the scent. Athletes learn to control their inhalation during intense exercise, breathing deeply and steadily to get more oxygen to their muscles.

The opposite is exhalation, breathing out. Together, these two actions make up the breathing cycle that keeps you alive every moment of every day. Doctors sometimes need to know about a patient's inhalation patterns to understand lung health, and singers train their inhalation technique to hold long notes. Your body performs this vital action roughly 20,000 times a day, mostly without you noticing at all.