Edit: I also did not find types of defense. Do they not exist anymore?
In P:K you had to look at dodge AC, natural AC, armor AC and so on. I also did not find touch attack or flat footed to see which armor can be used for defense.
I believe rules for defense were simplified in 5e because having a bunch of different rules which modify AC was confusing, and confusing bogs the game down. Now there's just AC - if your score with an attack roll (either ranged, melee or spell) plus modifiers meets or exceeds the target's AC, the attack hits and does damage. If the attack is less than AC, it does no damage.
