Defiant gear was introduced some time during the Secrets of Faydwer expansion pack and has a chance of dropping off almost every single enemy in the game that's below level 85. This gear was added into the game as a means of helping people who are trying to catch up to max level. Without the addition of Defiant Gear it would be nearly impossible to find enough decent gear in The Bazaar for someone looking to reach max level.
The Defiant Gear comes with useful focus effects on nearly every piece which will greatly bolster a character's strength as well as extremely high stats for that level range. If you're unsure what Focus Effects are I recommend you check out my Focus Effects Guide for more information. There are a total of 8 different sets of Defiant Gear for levels 1 - 80. A list of each set can be found below.
Crude Defiant Gear (Recommended level of 10. No required level.)
Simple Defiant Gear (Required level of 5. Recommended level of 20.)
Rough Defiant Gear (Required level of 15. Recommended level of 30.)
Ornate Defiant Gear (Required level of 26. Recommended level of 40.)
Flawed Defiant Gear (Required level of 37. Recommended level of 50.)
Intricate Defiant Gear (Required level of 48. Recommended level of 60.)
Elaborate Defiant Gear (Required level of 59. Recommended level of 70.)
Elegant Defiant Gear (Required level of 70. Recommended level of 80.)
Until you reach level 60 - 65 the Defiant Gear is some of the best gear you can possibly get for your character outside of old school raid gear that is droppable. Once you hit level 65 you'll start to notice the strength of Defiant really starting to drop off. At this point you'll need to transition to SoF group gear or something better.
Q: What expansion do I need to get this gear?
A: None, you can get it and equip it with any expansion.
Q: How expensive is this gear in the bazaar?
A: Usually it's extremely affordable which makes it some of the best gear you can get for leveling up until level 70 or so.
Q: How common is this gear?
A: By level 50 you'll probably see two dozen pieces drop.