What does vanilla mean?

Computer software, and sometimes also other computing-related systems like computer hardware or algorithms, is called Vanilla when not customized from its original form, meaning that it is used without any customizations or updates applied to it.

http://en.wikipedia.org/wiki/Vanilla_software

Vanilla often refers to pure or plain. So in terms of programming languages, it means either without the use of 3rd party libraries or without the use of frameworks.