Question

what is a pcb layout?

Answer 1

A PCB (Printed Circuit Board) a way of connecting electronic circuits elements together, it is that flat green thing you see with the components on it. A PCB is two dimensional board and that added constraints in connecting elements that aren't present in the schematic, also this is now the real world where two traces running next to each other on a PCB may act as a capacitance, or inductance this can cause your circuit to misbehave.
So PCB layout is the art and science of designing a board so that the circuit functions like the schematic that was designed.