CAT 5e / CAT 6 / CAT 6A

All three cable types are unshielded twisted pair (UTP) cables. They each utilize 4 twisted pairs in a common jacket. They use the same style RJ-45 jacks and plugs. And, they are each limited to a cable length of 100 meters including the length of the patch cables on either end of the link. The parts are interchangeable, so you can use a Cat5e patch cable with Cat6 house cabling. Your system will just perform at the level of the lowest link, in this case the Cat5e patch cable.
So what's the difference?
Better transmission performance. With each upgrade in cable, there is less signal loss, less cross talk, and a larger frequency bandwidth where performance expectations are defined. These are all electrical differences though, and don't neccessarily translate into faster performance. A common misunderstanding is, if you put in a higer grade of cable, you will get faster network performance.
The reality is, network speed is defined primarily by the electronic transmission equipment (the network switch, etc). A network switch will negotiate the fastest link it can manage, in increments of 10Mbit/s, 100Mbit/s, 1Gbit/s, or even 10Gbit/s. A switch or NIC card will start off trying for the best speed it is rated for (usually either 100Mbit/s or 1Gbit/s). If the other end, and the cable can't handle that speed, it will drop down to the next level. So.. if you buy a Gigabit switch, and have Gigabit NIC cards in your PCs, then you'll get Gigbait speeds so long as your cable supports that.
Here's what each cable type is rated for:
Cat5e:
  • Gigabit Ethernet up to 100 meters
  • 10 Gigabit Ethernet up to 45 meters
  • Cat6:
  • Gigabit Ethernet up to 100 meters
  • 10 Gigabit Ethernet up to 55 meters
  • Cat6a:
  • Gigabit Ethernet up to 100 meters
  • 10 Gigabit Ethernet up to 100 meters