ECO, short for Engineering Change Order, refers to the engineering change order.
In short, it is the process of manually modifying the integrated circuit, in other words, it is directly manually modifying the netlist.
Generally used in digital chip layout design. For digital IC design, the ECO step is actually an exception to the normal design process. It is a small range of local modification and rewiring of the layout of the design, without affecting the layout and wiring of other parts of the design, so the timing information of other parts has not changed.