I was wondering if there is an official definition for churning.

For the past 5 years or so my wife and I have opened 1 or 2 cards a year to take advantage of mile/point promotions (that we receive in the mail). We typically get the card for it's large opening bonus, spend with it until we reach a desired mile/point threshold for an award, and then close it after about a year before the annual fee comes.

To the best of my recollection, here are the programs we have joined:
2002: 1/2 mile UAL Visa
2003: Delta Amex
2004: AA Mastercard
2005: UAL Visa, Marriott Visa
2006: Starwood Amex, Juniper Usair, AA Mastercard

Would we be considered churners? Or is the term meant for people who open and close 10 cards a year or something like that?