Definition
The fundamental elements of a play.
The basic delineation of roles in a project.
Origins
Derived from the use of the letters X and O as common stand-ins for other concepts.
How People Actually Use It
Hugs and kisses. 'X' is for the crossing of the arms when one hugs another, and 'O' is for the shape of one's mouth for a kiss.
"Dear Love-of-my-life, (insert really sappy love letter-type thing here) X's and O's, (insert the sappy love letter's writer's name here)"
Source: Urban Dictionary