Ask Andy: What is 'dark pool' share trading?

Barclays Bank has been fined $70m (£48m) by US regulators for its handling of so-called "dark pool" trading. Credit Suisse has also been fined $60m for its involvement. But what exactly are "dark pools"?

That's a question for our Economics correspondent Andy Verity. That's because he'll be taking a regular look at some of the more esoteric phrases bandied around in financial circles. We thought we'd start him off with "dark pools". But there's a catch. He has to do it in as little time as possible.