The backpackers club in the UK has this to say:
No formal definition of 'Backpacking' exists, but perhaps a good description would be the art of being self contained, carrying everything you need to survive in the outdoors such as a tent, sleeping bag and food etc. whilst walking/cycling from one location to another on a multi-day journey through a natural landscape. A good example would be backpacking along a Long Distance footpath. This club is not to be confused with 'backpacker' who may travel by train/plane staying in hostels etc. The Backpackers Club is for those who propel themselves across the countryside whether by walking cycling, canoe or even cross country skiing!

SO backpacking has two meanings, that which we on this forum would generally use, and cheap (frequently urban) travel