It was intended to extract opinion from a group of experts, using the benefits of committees, while avoiding some of their disadvantages. Delphi is currently in wide use for preparing forecasts of technology, and for gathering policy information. I have used Delphi for over 30 years. A detailed description of the procedure can be found in my textbook, Technological Forecasting for Decision Making. Anonymity means that none of the panel members know specifically what other panel members have responded to the questions.
Iteration means that the process consists of a sequence of written questionnaires.
Persons on the panel are expected to answer each question, and to provide written statements supporting their positions. Controlled feedback means that the moderator screens out irrelevant or repeated statements, and provides the statements to all panel members on the next round of questionnaires. That is, if two or more panel members make the same statement in support of a position, it is included only once. Statistical response means that the panel is not required to come to a consensus. The final result is a statistical description of the panel's position on each question.