Privacy by design means that privacy must be the primary principle in designing and developing software, and should be assured by the way organizations operate. It has to be taken into consideration from the beginning of every project and throughout its entire lifecycle.
The concept was initially defined by Ann Cavoukian for systems engineering and has since been widely adopted by various organizations, becoming an obligation under GDPR. According to the Regulation, you need to incorporate safeguards into data processing from the initial phases of design of processing operations, both at the technical and organizational levels.
More about privacy by design on the Piwik PRO blog:
Privacy by design under the GDPR