hard-on - stiffy - boner - tumescence - engorgement - swelling - arousal - vertical position - upright position
An erection is a physiological process in which the penis becomes firm, enlarged, and elevated due to increased blood flow into its erectile tissue. It is typically triggered by sexual arousal but can also occur during sleep or without conscious stimulation. Erections are controlled by a complex interaction between the nervous system, blood vessels, hormones, and psychological factors. They are essential for penetrative sexual intercourse and are often seen as an indicator of male sexual health. Problems maintaining or achieving an erection can be a sign of physical or emotional health issues.