Channel

A channeled ability is any ability which, upon activation, makes the champion immobile and unable to attack or use abilities in order to achieve the desired effect.

Gameplay
All channeled abilities can be interrupted by enemy champions using any "interrupt" crowd control effect on the channeling champion. Interrupts do not include slows, blinds, or snares. They can also be interrupted by the player by giving orders such as walking away or activating another ability. Using most summoner spells will not interrupt channeled abilities.

Channels that can only be stopped by enemy crowd control or by the player's choice are called soft channels. However, ALL channels can be cancelled at the player's will through using the summoner spell. Although a rare occasion, the cancelling of a channel by using may be a preferred option when one starts a channel that will have an undesired result such as death.

There are other actions that produce a channel will be stopped by any damage dealt by champions. These are called hard channels. Hard channels include capturing or neutralizing nodes, capturing the Greater Relic on the in Dominion, and the use of recall. Damage caused by enemy minions will interrupt recall only.

Summoner spells
and are interrupted by any damage taken to the champion's life-bar directly. This means that shielded champions continue their channeling as long as the shield remains intact.

Champion abilities
These channels are indicated by a cast bar going right-to-left.

Pseudo-channels
Channelled abilities that can only be interrupted by the death of the caster

Absolute channels
Channeled abilities most notably attached to certain blinks or dashes. These abilities each reveal a cast bar that essentially denotes the duration of the ability's "start-up" animation. CC applied during these start-up animations do not interrupt the spell but still affect the target for the full duration. However, the target CC'ed during start up will essentially continue the animation while CC'ed and remain CC'ed for the remaining CC duration after the spell is completed.