In the Product Development Loop, implementation is manufacturing the object. For the lower levels loops, implementation consists usually in creating the data for manufacturing.
In IC design, the implementation phase consists in translating the sized schematic which is some sort of a symbolic description including architecture and sizing into a physical description. This phase called “LAYOUT” adds some specific constraints to the design.
Along the Architecture and Sizing phases, the design is usually a set o files in a CAD system.
While the schematic is a symbolic representation that does not take into account the relationship between components values and sizes and that does not consider topology, layout does. For instance, a resistor size in the layout depends on its value. This, of course has an impact on the topology.
Another constraint is that the layout is a 2D structure. The third dimension exists but the designer cannot play much with it.
During the layout phase, the design is usually a set of files in a CAD system. The difference with the previous phases lies in the kind of information the files contain.
In IC development, manufacturing is the implementation phase for the whole product.