CPU = Central Processing Unit - this is basically the brain of your computer. All instructions are run through and acted on by the CPU. Faster CPU's tend to be able to process more in the same period of time as slower CPU's (there are caveats, but that's beyond this basic description). CPU's range from single core and up. In Mac's these days they range from dual core up to quad core for the mini, iMac, air and Macbook Pro and from quad to 12 in the Mac Pro. To learn more about CPU's see:
Central processing unit - Wikipedia, the free encyclopedia - what level of CPU you need is really heavily dependent on what you do and what the software you are using requires and/or recommends to get a quality user experience.
GPU = Graphics Processing Unit - these are specialized cores designed for graphics / display rendering. They allow for hardware decoding of video, 3D graphics acceleration, displaying your desktop, etc. There are two major kinds of GPU's -
integrated (on the motherboard or CPU) like the HD3000 or HD4000 and
dedicated like the 650M. There are also hybrid systems that have both integrated as well as dedicated GPU's and have the capability of switching between the two depending on the workload given to it. Dedicated GPU's tend to be more powerful (detailed description on why they are more powerful is beyond this basic description) and have dedicated high speed RAM that allows for higher frame rates, faster rendering, etc. than their integrated counterparts that will share system RAM (for example, a current (this year) Macbook Air with 8 gigs of ram will share 512megs of it with the integrated HD4000 GPU, this sharing of system RAM can negatively impact graphics performance in higher demand applications (real time rendering, real time effects in video editing done in FCP, gaming, etc.)). To learn more about GPU's see:
Graphics processing unit - Wikipedia, the free encyclopedia - people who tend to worry about higher end GPU's are those that either need the rendering capabilities for work or play; average users usually don't require super high end GPU's.
FCP = Final Cut Pro - the professional grade video editing tool from Apple. Current release on the App Store is Final Cut Pro X. The previous version was version 7 which was part of the Final Cut Studio 3 suite. To learn more about Final Cut and its history see:
Final Cut Pro - Wikipedia, the free encyclopedia