'boot' means to turn on a computer.
're-boot' means to turn a computer off-and-on.
This comes from the expression: "Pull yourself up by your own bootstraps."
and from the computer term: bootstrap program.
This blog is mainly to explain a different English language expression every day. Sometimes I post other stuff. I also have a YouTube channel which is mostly about computer software: https://www.youtube.com/englishspacedog
