Short answers, pulled from the story.
Angular momentum acts as the rotational counterpart to linear momentum. It depends on the origin point chosen in space and equals the cross product of position and momentum vectors for a single particle.
R.B. Hayward introduced the specific term angular momentum in an article published in 1864. Before this period, English speakers typically referred to the quantity as momentum of rotation.
Tidal forces transfer angular momentum from Earth to the Moon, causing Earth's rotation to slow down while pushing the Moon into a higher orbit. Measurements show the day lengthens by approximately 1.7 milliseconds every century due to these exchanges.
Figure skaters increase their rotational speed because their total angular momentum remains constant throughout the motion. When they reduce their moment of inertia by drawing limbs closer to the vertical axis, their angular velocity must rise to compensate.
William J.M. Rankine defined angular momentum in its modern sense within his Manual of Applied Mechanics from 1858. He described it as a line whose length corresponds to magnitude and direction lies perpendicular to the plane of motion.