PB - printed board. the most generic term for a bare board
PWB - printed wiring board, one of the first uses when the issue was only a point to point connection.
PCB - printed circuit board, where the width, side to side and multi-layer relationship(spacing) of conductor runs has or is designed to have a specific effect on circuit operation other than just a point to point connection. Circuit impedance is a primary issue. In approximately 1999 the IPC Technical Activities Executive Committee made a mandate to only use the term PCB for all new document development because more often than not the printed circuitry design will have an impact on function.
PWA - printed wire assembly - older use
PCA - printed circuit assembly - logical to use with the 1999 change to PCB.
PCBA - printed circuit board assembly - multiple requests/comments (strong push) from users and technical committees in Asia and Europe to use this as the preferred term.