It refers to BF Skinner’s innovation to help improve teaching that is based on his theory of verbal behavior as an augmentation aid to traditional education.
Programmed Instruction is a form of operant conditioning. It involves the breaking down of content into small sections, frequent questions, immediate feedback and self-pacing approaches and must progress from simple to complex. This method was later adopted and developed further by American psychologist Robert Mills Gagné to form his method of Programmed Learning which is geared toward teaching facts (while the former is concerned with modifying behavior).
They key to Skinner’s idea is that of continual strengthening of stimulus-response bonds using appropriate rewards/punishments. The principles of programmed learning are now applied in the field of Computer Assisted Instruction.