I'm reading about ColdBox, and I came across this word.
So what is meant by convention based framework?
Like BitOff mentions, it means what others convention over configuration. This seems to be confirmed by the ColdBox home page.
Basically, this means that instead of having configuration files describing details about a project - where to find files, which classes to instantiate, which URLs map to which classes, and so forth - the framework provides good defaults that allow you to just put the files and classes and methods in the right place and be done with it.
It means that details that usually do not carry any semantic (that is, any meaning) are used by the framework to generate a default configuration. It is also known as "convention over configuration".
For example, in Ruby on Rails, if you use a class named Customer, the generated database table will automatically be named "customers".