Short answers, pulled from the story.
Johannes Kepler derived the word satellite from the Latin term satelles meaning guard or attendant. He published a pamphlet in 1610 titled Narratio de Observatis a se quatuor Iouis satellitibus erronous to describe four objects orbiting Jupiter that Galileo had discovered earlier that same year.
Artificial satellites changed everything when Sputnik launched in 1957. Engineers needed a way to distinguish man-made objects from celestial ones and quickly abandoned phrases like artificial moon to settle on simply calling them satellites.
Irregular satellites often travel on distant inclined eccentric or retrograde paths around their hosts while regular satellites follow prograde orbits that are circular and uninclined relative to the equator of their primary body. Scientists believe these wanderers were captured asteroids that fragmented further through collisions.
Neptune's moon Proteus holds the title of largest irregularly shaped natural satellite. It measures roughly as large as an icy body can grow before relaxing into a spheroid due to hydrostatic equilibrium causing synchronous orbit shapes to asymptotically change toward rounded ellipsoids over time.
Tidal heating powers geological processes for these three bodies through eccentric orbits near giant planets. This mechanism operated on Triton before its path circularized and continues today across several large moons despite billions of years passing since formation.