Core was the microarchitecture for Intel's 65 nm process for desktops and servers as a successor to NetBurst. Core was replaced by the Penryn microarchitecture in late 2008.
When Core was introduced in 2006, Intel described it as a merger of both P6 and NetBurst. When scrutinizing the details, it's fairly clear that little was actually borrowed from NetBurst. In fact, it wasn't until Intel's entirely new microarchitecture Sandy Bridge that a true merger presented itself.