Definition
Boot "represents the automatic start-up process when the computer is turned on. A computer usually boots from its hard drive."[1]
To boot is "[t]o initialize a computer system by clearing memory and reloading the operating system."[2]
To boot is "[t]o cause a computer system to reach a known beginning state."[3]
Overview
"A boot program, in firmware, typically performs this function which includes loading basic instructions which tell the computer how to load programs into memory and how to begin executing those programs."[4]