The use of the word dimension here more than likely stems from dimensional modeling / data warehouse / OLAP design [1], where designing your database in a star/cube schema will allow you to query it easily across many "dimensions".

With crossfilter.js your data gets structured similarly and then bound to d3.js svg charts. dc.js provides the glue between the two to make it easier to work with. This allows you to interactively select part of a chart and immediately see other charts bound to that data get filtered at the same time.

It allows for an interesting way to explore / visualize data.

[1] https://en.wikipedia.org/wiki/Dimensional_modeling

Lol, I thought it was D3 Charts :)