Communicating so that a highly complex stimulus in which two mutually incompatible frames of reference are linked together, producing a physiological reflex, laughter. It serves both the physical and psychological functions of releasing surplus tension.
Since humour depends so heavily on shared frames of reference, it is difficult to apply cross-culturally.
Humour allows potentially dangerous tensions to be dissolved.
Threatening people, issues or social institutions are brought to a level at which they can be approached as equals.
Life does not cease to be funny when people die; any more than it ceases to be serious when people laugh. (George Bernard Shaw).
What I want to do is to make people laugh so that they'll see things seriously. (William K. Zinsser).
Humour can be dissected, as a frog can, but the thing dies in the process and the innards are discouraging to any but the purely scientific mind. (E B White and Katharine S White).
Humour only creates the milieu in which dialogue and openness are possible.
It is common to "laugh off" issues that in fact require further strategies to be resolved.
Humour can be exclusive, causing more tension than it dissipates, with "inside jokes".