Heavily-laden
cross-country walking. The term is British military slang, popularized in the
Falklands War when troops (
2 Para and the
Royal Marines) were landed at
Goose Green to capture that and then had to cross the
boggy island to take
Port Stanley.
It originally meant the walking was performed laden with full kit. Synonym as such: forced march, road march, and slang humping and ruck hump. Yomping at twice the speed is called tabbing.
Since then it seems to have entered the popular vocabulary as some kind of more or less strenuous cross-country leisure activity, on a par with hiking or trekking. The difference perhaps is that while hiking you're allowed to stop for a two-hour lunch in a pub, and trekking is done in exotic places, but yomping requires a good filthy bog to feel you've got the most out of it.
Although... The third reference below uses it merely to mean "walking around with a rucksack, because they're in Paris: "The next couple of hours were spent yomping around in search of a room."
Almost always found as participial "yomping", but the verb and noun "yomp" also occur.
www.cadetstuff.org/features/200202/200202_winter_hawk_glossary.htm
www.odps.org/slangy.html
www.sff.net/people/sanders/par1.html
Ack! The node yomp already existed but searching for "yomping" didn't find it. /me complains to nate.
Editor's note: As outlined by Lucy-S at SFF Net, the site referenced above has gone offline. As of March 2017, you can find the referenced article at http://www.mrbadexample.com/sanders/par1.html.