The common definition of 'code drop' is to deploy new or updated application code. Stems from the usage of "drop boxes" to deposit said code onto, from which an automated system or an engineer deploys the code in some useful or not so useful manner. "Code drop" can refer to the placement of code for a deployment, or it can refer to the actual process of deploying the code, also called a code deployment.
coworker 1: "What's a code drop?"
coworker 2: "Shit man, google yo!"
<1 minute later>
coworker 2: "Crap, there's no easily accessible definition on the web, I'll urbandictionary it."
coworker 1: Hey, can you take this code drop?
coworker 2: No way man, that application is always broken. I'm not sticking my hand into that hole.
coworker 2: What are all these <application name> alerts coming from??? Who broke <application name>???!
coworker 1: Shit, it must have been bad code in that code drop I just deployed!
coworker 1: Shit, it must have been my code drop!
coworker 1: Fuck, we're all dead! That was the reactor core regulator code!