Definition:
White space is used in conversion optimisation as a directional cue that subtly directs user’s attention towards an important area of the page (e.g. the call to action). Also see directional cues.

Resources:
Conversion marketing – Glossary of Conversion Marketing.
Over 300 tools reviewed – Digital Marketing Toolbox.
A/B testing software – Which A/B testing tools should you choose?
Types of A/B tests – How to optimise your website’s performance using A/B testing.