What does mega mean in Internet?

Excuse me, could you clarify for me what the term "mega" actually signifies when used in the context of the Internet? I've come across it numerous times but have yet to fully grasp its precise meaning or purpose within the digital realm. Perhaps it's related to a specific unit of measurement or a way to denote a certain level of significance or size? I'd appreciate it if you could shed some light on this for me.