What is "inner core"

n. 1 (&lit inner core English) 2 (context planetology English) The solid material found in the centre of some planets at extremely high temperature and pressure, distinct from the liquid outer core. 3 # (context geology English) The innermost part of the Earth, believed to be made of a nickel-iron alloy.

The Earth's inner core is the Earth's innermost part and according to seismological studies, it has been believed to be primarily a solid ball with a radius of about 1220 kilometers, or 768 miles (about 70% of the Moon's radius). It is composed of an iron– nickel alloy and some light elements. The temperature at the inner core boundary is approximately 5700 K (5400 °C).