I heard that it's more of a platform than a processor. Can anyone elaborate?
The Celeron is simply a mainstream chip with things turned off, reduced cache, and reduced clock speeds to make it a budget chip. I think the "platform" thing you're thinking of is "Centrino," which is Intel's mainstream mobile platform (Intel Pentium M/Core/Core 2 CPU + Intel IGP + Intel wireless card).
As a side note, some Celerons are decent and some suck. The current desktop Celeron 400 series is decent if you want a very efficient single core. The dual-core Celeron E1000 series isn't so great as they have so little L2 cache that performance is much poorer than equivalently-clocked Pentium Dual Core or Core 2 CPUs. I'd also avoid the Celeron M laptop CPUs as they lack SpeedStep and will constantly run at full voltage and full speed and eat your battery much more quickly than a SpeedStep-enabled Pentium Dual Core or Core 2 CPU.