The minimum speed needed to escape a body's gravity well without any further thrust, the first step to leaving any world behind.
Log scale: the Sun is shown at full width; it would be completely off-chart on a linear scale.
G = gravitational constant (6.674 × 10⁻¹¹ m³ kg⁻¹ s⁻²)M = mass of the body (kg)r = radius of the body (m), or distance from the centerve = √(2gR) where g is surface gravity and R is radius.√2 ≈ 1.414× the circular orbital speed at the same altitude. A spacecraft doesn't need to reach escape velocity instantly (it can use continuous thrust), but at escape velocity with no further thrust, gravity can no longer pull it back.