Trucking is the business of moving goods from place to place by road, in trucks. It is an industry word: *the trucking industry*, *a trucking company*, *trucking costs*, *he works in trucking*. Notice that it names the whole activity as a business or field, not one journey — you would not say "the trucking took six hours"; you would say "the drive" or "the delivery". Like *trucker*, it is American; British English says *haulage* or *road haulage*. It is also simply the -ing form of the verb *truck* (to carry goods by truck), so you will see it as an ordinary verb too: "They were trucking supplies across the border." That verb use is much less common than the industry noun. One thing to know because your students will hear it in songs and films: *keep on trucking* is an old American slang phrase, from the 1970s, meaning "keep going, don't give up, keep living your life the way you do." It has nothing to do with trucks by then — it is pure encouragement, and it sounds cheerfully out of date, which is often exactly why people say it.