An EtherChannel is the aggregation of multiple physical links to provide redundancy and increased bandwidth between the devices. EtherChannel bundles can have up to eight physical ports of the same speed and media type, depending on the switch capabilities.
EtherChannels can be negotiated using either one of these protocols:
Port Aggregation Protocol (PAgP) (Cisco proprietary)
Link Aggregation Control Protocol (LACP) (IEEE 802.3 ad)