There are some terms in Connect came up pretty often, but don't have an explanation in one location. Usually these came from IEEE 802.15.4, and most of them related to addressing. Here are a short explanation of some of these terms:
Channel: Most PHYs available in Connect provide multiple channels to use. There's no communication between channels, so if you transmit on channel 2, only a receiver tuned to channel 2 can receive it.
PAN: Personal Area Network. In this case, it's equivalent to a Connect network. Note, that there can be more than one PAN in the same physical area, using different PAN ID.
PAN ID: Identifier of the PAN, uint16_t. Using different PAN IDs, multiple networks can coexists in the same area. Think of PANs as virtual or software implemented channels. In 802.15.4, it's possible to have the destination in different PAN than the source, but that's not allowed in Connect.
Long address or EUI64: uint64_t address, globally unique. Follows the same format as the MAC address used in IPv6.
Short address: uint16_t address, only valid inside the PAN. Since 802.15.4 frames have a limited length (to 127B), it's a good idea to not use 8B long addresses, especially in frames that require both source and destination address (usual for data frames). This is why the short address exists. The short address is assigned by the PAN coordinator, which is the coordinator in connect star topology networks.
Special short address 0xFFFF: Broadcast address in the PAN
Special short address 0xFFFE: No short address assigned yet (typically because not joined to any PAN yet)
Special short address 0x0000: (this is not 802.15.4 related) Address of the coordinator in Connect star topology network
Endpoint: (this is not 802.15.4 related) Similar to TCP/IP ports. Helps the application to assign different endpoints to different application usage. Type is uint8_t.
802.15.4 allows multiple type of addressing, but connect applications for now only use intra-PAN messages. This means that you can only send application data inside a PAN, source and destination identified by the short address, PAN ID in the message both the source and the destination's PAN. Other addressing methods are used when an end device joinins to a coordinator.