Number of Servo's Attached to an Arduino.

Just a quick question that I'm struggling to get a straight answer from the intertubes about...

I'm looking at purchasing an arduino board to control some servo's, and wondering how many each can control?

For example: Uno R3 has 14 digital i/o pins (6PWM outputs), and 6 analog inputs. What does this mean exactly?

[original story: Let's Make Robots]