iBeacon™ is a trademark registered by Apple and refers to how Apple’s iOS devices detect beacons. Apple was the first smartphone manufacturer to include BLE in their iOS operating system as iBeacon which is a software extension of the BLE protocol. While BLE defines the data transmitted and the RSSI signal strength, iOS calculates the actual distance and delivers to the application the calculated values so the developer does not have to rely on RSSI calculations. Android programmers don’t have that luxury and have to base their distance calculations on the RSSI signal which can vary depending on manufacturer of the device.
At hardware level, beacons are BLE devices broadcasting data. At software level, beacons are messages sent by broadcasting devices, that are then detected and processed by receiver devices, like a mobile app running on iOS. These data are considered beacons as well, depending on how you name things.