What is the very small faint hot star?

A very small, faint hot star is typically referred to as a "white dwarf." These stars are the remnants of medium-sized stars that have exhausted their nuclear fuel and shed their outer layers, leaving behind a dense core. White dwarfs are extremely hot initially but have low luminosity due to their small size, making them faint compared to other stars. Over time, they cool and fade further, eventually becoming undetectable.