A spinning neutron star is known as a pulsar. Neutron stars are incredibly dense remnants of massive stars that have undergone a supernova explosion. When a neutron star rotates rapidly, it emits beams of radiation from its magnetic poles. As these beams sweep across the line of sight of observers on Earth, it appears as periodic pulses of light, leading to the name "pulsar." These pulses can be detected across a wide range of wavelengths, from radio waves to X-rays.

Option 1: A white dwarf is a dead star that has burned out and collapsed, but it is not a spinning neutron star.

Option 2: A black hole is a region of spacetime where gravity is so intense that nothing can escape, including light. While pulsars can form from the remnants of massive stars collapsing into black holes, a spinning neutron star is not a black hole.

Option 4: A quasar is a highly energetic and distant active galactic nucleus, and it is not a spinning neutron star.

Therefore, the correct answer is option 3: Pulsar.