A single customer view (also called ‘360’ or ‘unified’ customer view) is a method for gathering all available data about your customers and merging it into a single record. This data comes from your website, mobile app, social media and your offline store.
The user record can include:
Online and offline user data (browsing history, Conversion),
Transaction data (purchases and sales)
Personal data (names, addresses, social media)
More about single customer view on the Piwik PRO blog: