Trivial question about naming convention that you may roll your eyes at: Why "z"?

[DigitalNaut]

For context, even though I've been programming for some time, I'm kind of new to this whole web dev so I feel like I'm missing something here. I also don't know if this type of question is allowed here, so forgive me if it's not.

That said, I'm seeing this trend of using single-variable names for library objects, both on Zod and tRPC that uses "t" on the server side but not the client side. I'm wondering if it's something new or if it's a vestigial from other programming languages. Is it just a popular trend with the cool kids?

For clarification: I know that I can name it whatever I want, but I'm talking about the documentation specifically. Also, yes, this question does not let me sleep at night. 😂