I would check out chapter 2 when you get a chance for details about what you can do with Mondrian (or buy the book!). http://www.manning-source.com/books/back/MiAch02sample.pdf
In a nutshell, Mondrian is an engine for doing multi-dimensional analysis. So if you want to look at sales data, for example, you can answer questions like: how many products of each type did I sell last quarter, or who are my most profitable customers. The key is that the questions aren't known in advance. Mondrian provides an infrastructure for users to be able to ask their own questions against the data without having to write code or SQL queries.
It differs from big data in that it is not a storage mechanism, but rather a way to access information about the data. It differs from machine learning in that it's a tool for analysts.