The "Merom" processor is the next iteration of the Core series of Intel processors, an extension of the "Yonah" Core Solo and Core Duo processors currrently in Intel Macs and many other computers. The terms "Merom," and "Yonah" are Intel codenames for the processors while they were under development. There's no such thing as a "Celeron Core Duo" chip.
Read
this forum thread for an explanation of these different processors, at least to some extent.
The Core series is an outgrowth of the Pentium 3 (NOT the Pentium 4!) series processors, but with enhancements that make it smaller, and MUCH faster.