Unfortunately the 2 phrases are used interchangeably.
Historically, SPC referred to statistical process control charts. (Also referred to as control charts and behavior charts)
SQC referred to the whole range of statistical quality tools: Design of Experiments, Guage R&R, Acceptance Sampling as in the Western Electric manual. Then Ellis Ott published a similar book with those topics and called it Process Quality Control, so really the terms have become synonymous.
Historically, SPC referred to statistical process control charts. (Also referred to as control charts and behavior charts)
SQC referred to the whole range of statistical quality tools: Design of Experiments, Guage R&R, Acceptance Sampling as in the Western Electric manual. Then Ellis Ott published a similar book with those topics and called it Process Quality Control, so really the terms have become synonymous.
