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The Big Bang is the leading explanation about how the universe began, positing that it started from a singularity roughly 13.8 billion years ago and has been expanding ever since.

A black hole is a region in space where the gravitational pull is so strong that nothing, not even light, can escape from it. It is the result of the collapse of a massive star.

Redshift refers to the phenomenon where light from distant galaxies is stretched to longer wavelengths (and towards the red end of the spectrum) due to the expansion of the universe.

In the context of black holes, a singularity is a point where the curvature of spacetime becomes infinite and gravitational forces are infinitely strong.

An event horizon is a boundary around a black hole beyond which no information or matter can escape, marking the 'point of no return' for objects that fall into a black hole.

The CMB is weak cosmic radiation that fills the universe and is considered a remnant from an early stage of the universe in Big Bang cosmology.

A quasar, or quasi-stellar object, is an extremely luminous active galactic nucleus (AGN), powered by a supermassive black hole at the center of a galaxy that is accreting matter at a high rate.

The multiverse theory is a hypothetical group of multiple universes, which encompasses everything that exists: the entirety of space, time, matter, and energy as well as the physical laws and constants that describe them.

Dark matter is a form of matter thought to account for approximately 85% of the matter in the universe, affecting its structure and evolution through its gravitational effects despite being invisible because it does not emit light or energy.

The cosmological constant is a value representing the energy density of space, or 'dark energy', that is used in Einstein's field equations of General Relativity.

The cosmological principle is the assumption that on a large scale, the universe is homogeneous and isotropic, meaning it looks the same in all directions and from all points.

Hubble's Law is the observation in physical cosmology that galaxies are moving away from each other at speeds proportional to their distance.

Dark energy is an unknown form of energy that is hypothesized to permeate all of space, tending to accelerate the expansion of the universe.

General Relativity is a theory of gravitation that was developed by Albert Einstein, positing that gravity is the result of spacetime being curved by mass and energy.