Trek: "to go, especially on foot." That's one of Webster's definitions, but to the trekker the word also spells excitement, adventure, challenge -- and perhaps a time to test oneself.

To enjoy trekking, however, it is not necessary to rough it in the icy vastness of the Himalayas. Nor is it essential to be as knowledgeable and hardy as an expert mountain climber -- though you should be in reasonably good health, limber and prepared for local conditions.

A number of tour operators now offer well-designed packages with guides that enable the inexperienced trekker to savor a personal adventure in many areas of the world with minimal risk. Among the rewarding -- but not especially demanding -- trips scheduled for this year are:

* "McGee Basin Wilderness Threshold." This eight-day journey, one of many offered by the Sierra Club, is described as a good first hiking/camping experience for families. Limited to 30 people, with a minimum age of 8, the group will enter the Canyon de Chelly at Chinle, Ariz., on Aug. 2. Guides are the trip leaders (a husband-and-wife team) and Navajo Indians. All tents and gear will be moved by trucks with each change of campsite, so trekkers need carry only a daypack ; there will be about three to five hours of hiking a day on six days. Price: $935 for two parents and one child, each additional child $235. Everything is included except transportation to and from Chinle. More information: Sierra Club, 530 Bush St., San Francisco 94108, (415) 981-8634, ext. 527.

* "Discover Kenya." The 20-day package includes a seven-day hiking traverse of Mount Kenya -- with guides, porters, cooks and tents -- and a three-day "foot safari," a walk in Tsavo National Park through some of the wildest bush country in Kenya, with guides, cooks and tents. (Travel time and other activities fill the other days.) Departures from the U.S. will be on July 13, Aug. 10 and Dec. 15. Land cost only, excluding air fare: $1,950, per person, double occupancy. Mountain Travel, 1398 Solano Ave., Albany, Calif. 94706, (800) 227-2384.

* "Hiking the Swiss Alps." During five days of a seven-day package, the group will walk 45 miles in the Valais district and cover part of the Upper Rhone Valley. Participants will cross glaciers and wild mountain valleys, spending their nights in lodges and huts along the route. All luggage except day gear is transported by Jeep. Departures from Sion, which is two hours by train from Geneva and four hours from Zurich, on July 13 and Aug. 10. Land cost only, excluding air fare: $495 per person double occupancy. Sobek, Angels Camp, Calif. 95222, (209) 736-4524.

* "High Sierra Backpacking." These five-day treks are on established trails within the Yosemite National Park area, at altitudes ranging between 4,000 and 6,500 feet. Groups, limited to a maximum of 12, meet at Walnut Creek, Calif., or other selected location. Participants carry their own gear plus a share of the camping equipment and hike about four to five hours daily, trekking a total of 35 to 50 miles -- depending upon trail condition/selection. Part of the emphasis is on learning to work together as a team to accomplish group goals (traversing terrain, setting up camp, food preparation). There are two departures, July 4 and Aug. 19. Land cost only: $185 per person, includes all food, park fees and guides, but excludes personal camping equipment and transportation to meeting point. All-Outdoors, 2151 San Miguel Dr., Walnut Creek, Calif. 94596, (415) 932-8993.