PCB = printed circuit board, PCBA = printed circuit board + components

When it comes to PCB and PCBA, we have to mention SMT. SMT is a surface assembly technology. It is a popular process technology that mounts electronic components on PCB boards through a process, also known as surface mount technology. PCBA is the general term for a series of operations such as SMT patch, DIP plug-in, testing, assembly, etc. on the circuit board.

So: "PCB is a board, SMT is a technology, PCBA is a process or finished product", on a PCB board, SMT patch (or DIP plug-in), the obtained finished product can be called PCBA, or this process can be called PCBA. To put it another way, PCB is a bare board, PCBA is a finished board....

This is PCB:

This is PCBA: