These are code-names to differentiate between different CPU architectures. For example, Conroe is the code-name for Intels up-and-coming Dual-core CPU. Manchester on the other hand, is AMD's current Dual-core CPUs with 2x512KB of cache (The X2 4200, 4600, and maybe the 3800). Toledo on the other hand refers to AMD's dual-cores with 2x1MB of cache (X2 4400, & 4800).
This style is used to help people talk about difference CPUs that are the same, except for the clock speed, without having to actually list each processor model individually.
(Man, I thought you'd beable to find a nice comprehensible list of current code names on the net, but it's not coming up for me).
a decent list about the different codenames for AMD's current line up of chips.