A shout is a form of communication. When an adventurer shouts something, his or her voice is projected so that everyone on the same continent (not plane) will hear it unless they are deaf or have the shout channel turned off. Until an adventurer has reached level 100, he or she must use either a giant ram's horn or the ram's horn artefact to shout. Other beings may shout as well, such as denizens or Immortals, who are not limited to such handicaps.
The person doing the shouting will not be recognised unless the hearer is a God or has the recognition ability in Vision. What a shout sounds like will be characterised by the shouter's level. For example, a lower-level person might have "a weak and feeble voice" while a higher-level adventurer might shout with "a powerful female voice".
It should also be noted that a shout can only be of a finite length. Attempting too lengthy a shout will cause an adventurer to momentarily pass out.