How many digit is mega?

Excuse me, could you clarify something for me? In the context of cryptography and especially when discussing the security of various encryption algorithms, I've come across the term 'mega' being used to describe the strength or complexity. However, I'm a bit confused about the exact meaning of 'mega' in this context. Specifically, when we talk about 'mega' digits or 'mega' encryption, how many digits or what specific level of complexity is it referring to? Is there a standard definition or does it vary depending on the context? Thank you for your help in clarifying this.