Quite simply - it's the idea of visiting as many countries as you can.
A holiday, or even a day trip to a country is acceptable, but transiting an airport or port does not count - Visiting Changi Airport is not the same as visiting Singapore - staying overnight is NOT necessary, but it would be best if you could.
Having to obtain a visa, or getting a stamp in your passport (even if by request) certainly does count!
Country Bagging is NOT just a question of getting more countries, or doing it more quickly than someone else. Quality is just as important as Quantity.
In February 2006 after 10 years of travel, I took a little trip around the Arabian Gulf.
By traveling to Yemen, Qatar and Kuwait I managed to complete my "Alphabet of Countries" (the mad idea of visiting a country whose name starts with each letter of the (English) alphabet). I had three letters to go Q, Y and K, it seemed fitting to finish them all off in one go.
I'm quite happy that I've achieved my goal, and I'm not looking to take on any more challenges right at the moment - I think that the Alphabet of Capital Cities won't be completed for quite some time. Mind you I only have four 'capital' letters (F, I, Q and Y) to go. There is no capital city that starts with X. Clicking on the 'Countries' or 'Capitals' links on the left hand side will show where I've been.
14 Jul 12 - added the Lundy '12 Diary