Men think about power vertically -- and focus on rank and status and size. Women think about power horizontally -- it's largely about influence. I know I'm in trouble already. This is a stereotype, indeed. But in more than a decade of asking women leaders -- and the men they work with -- how they define power, I've discovered this to be an remarkably consistent truth. My favorite definition of power, actually, is one that Oprah Winfrey told me a few years ago. "Power," she said, "is the ability to impact with purpose."

Click on these links to see a terrific photo essay and video excerpts of this brand of power in action. Fortune's global mentoring program matches participants in our annual Most Powerful Women Summit with rising-star business women from across the developing world. We launched the program with the U.S. State Department three years ago. Fortune provides the mentors. The State Department, working with its embassies around the globe, supplies the mentees.

The mentoring program has expanded each year, and this past May, it was our most successful so far. Our 40 mentors included many of our MPWomen stars: CEOs Anne Mulcahy of Xerox (XRX), Andrea Jung of Avon (AVP), and Ann Moore of Time Inc. (Fortune's parent), plus the most senior women executives at such companies as Avaya, Ernst & Young, Exxon Mobil (XOM), Herman Miller (MLHR), KPMG, Merrill Lynch (MER), Microsoft (MSFT), and Wells Fargo (WFC). General Electric's (GE) top-ranked woman, Charlene Begley, mentored a woman from Zimbabwe. (We had two remarkable mentees from that desperate African nation.) Wal-Mart's (WMT) top woman, Linda Dillman, hosted a Peruvian entrepreneur in Bentonville, Arkansas. DuPont's (DD) most senior female execs mentored a biotech company boss from India.

For the first time, Goldman Sachs (GS) participated. And thanks to managing director Dina Powell, who helped start the mentoring program when she was an Assistant Secretary of State, Goldman is aligning with us to present an annual prize, the Goldman Sachs-Fortune Global Women Leaders Award. This award will go to one mentee who best employs what she learned in the U.S. to improve conditions back in her home country.

The first award winner will be announced October 1 at the Fortune MPWomen Summit in North San Diego, California. My mentoring program co-chair, Carrie Welch, formerly of Fortune and now at the International Rescue Committee, and I -- along with 250 remarkable women leaders -- will be celebrating the power that comes from women reaching across borders.

P.S. Postcards, at its best, is about insights into and from powerful people, plus doses of career advice. For a great take on all that, read Avon CEO Andrea Jung's Guest Post at the top of this page. It's called "Fire Yourself." It's both brave and really smart.