MBSSIDs (Multiple Basic Service Set Identifiers) – in short: Virtual AP’s. One physical device pretends to be multiple access points.
Trunks need to be used between the Distribution System and the WLC so SSID’s can be mapped to VLAN’s using 802.1q tagging. However, Lightweight AP’s can be connected to the DS via an access point and don’t even need to be in the same subnet as the WLC so long as they know the IP address of the WLC and routing between the two is good.
Autonomous AP’s need to be connected to the DS using trunks as there is no CAPWAP in use so traffic must be tagged between AP and Switch.
H-REAP – Hybrid Remote Edge Access Point – Lightweight Access Point usually across a slow WAN link that allows local breakout to save traffic having to go all the way back to the controller. Also connected via trunks.