CLI - Command Line Interface a tool that is used on the command line or terminal e.g. npm to install packages
GUI - Graphic User Interface
API - Application Programming Interface is a set of features and rules that exist inside a software program enabling interaction without it through software. In web development it is usually a set of code features developers can use in their apps for interacting with components of web browser or other software/hardware on user PCs or third party sites e.g using twitter API to retrieve data from user account to display their latest tweets on a webpage.
1st class functions - This is when functions in a language are treated the same as any other variable e.g. a function can be passed as an argument to other functions can be assigned as a value to a variable or returned by another function.
JIT (just-in-time) - This is a way of executing computer code involving compliation during the execution of a program - at run time - rather than before execution.