Axial tilt, also known as obliquity, is the angle between a planet’s rotational axis and its orbital axis. Earth’s axial tilt is approximately 23.5 degrees, which is responsible for the seasonal variations in climate. Changes in axial tilt over geological timescales can influence climate patterns and are a key factor in the study of Earth’s paleoclimate.
Reference: Laskar, J., Robutel, P., Joutel, F., Gastineau, M., Correia, A. C. M., & Levrard, B. (2004). “A Long-Term Numerical Solution for the Insolation Quantities of the Earth.” Astronomy & Astrophysics, 428(1), 261-285.