A pair of terms coined by Moyra Turkington on her blog, "Space and Death", in January 2006 -- clarified in May 2006.

Push is an assertion of individual authority. A player, using a Push technique, uses his own authority to put something out there. This something could be an assertion of an element or action into the fiction, it could be something in the social contract that causes or prevents something from happening (E.g. identifying that a personal line has reached a hard stop) or in other ways.

In contrast, Pull is a directed solicitation for collaborative buy-in and input. A player, using a Pull technique, solicits another player’s buy-in or input. This can happen by catering input to the other player’s tastes, by enticement, by reward, by negotiation, by collaborative mutual decision (and I’m sure there are other ways). Pull can be used to influence the fiction, but Pull techniques are not limited to the fiction.

References:

• Push vs. Pull (Moyra Turkington, Jan 2006)
• Pull Clarification and Promises! Promises! (Moyra Turkington, Jan 2006)
• Saurashtra - Actual Pull Play Examples (Moyra Turkington, Jan 2006)
• Push and Pull: An Example (Brand Robins, Jan 2006)
• Pulling Coplayers In (Vincent Baker, Jan 2006)
• Push/Pull and Additive/Negational (John Kim, Jan 2006)
• Push/Pull, Yin/Yang, and All That Jazz (Jonathan Walton, Jan 2006)
• Push Me, Pull You" (Joshua BishopRoby, May 2006)
• Push and Pull- Let's nail this down (Chris Chinn, May 2006)
• Clear and Concise Actual Play Examples of Push/Pull (StoryGames discussion, May 2006)
• Push and Pull - Trying one last time (Moyra Turkington, May 2006)
• Push and Pull: Appeals to authority (Thomas Robertson, May 2006)
• Push|Pull: The Moment of Crisis (Brand Robin, May 2006)