Common Lisp is a general-purpose programming language with functions as first-class citizens. Don't worry about being purely functional, Lisp is Object Oriented too. CLOS is a very powerful object-oriented system!
The Common Lisp lingo is quite unique:
- Package: Basically a namespace, a place for symbols to live
- System: Basically a Library. A bunch of code plus some instructions how it should be treated, for example which other systems it depends on, what should be loaded and/or compiled first, etc. Not in ANSI lisp but widespread. The most common system definition tool is ASDF.
- Modules: Deprecated and implementation-dependent
- Quicklisp: Like NPM or Ruby Gems for ASDF Systems.