means Going on a long, strenuous journey on foot, typically over rough or wild terrain and often for several days at a stretch.

from A gift from Afrikaans, where trek meant a journey or migration by ox-wagon — the slow, grinding hauls of the Voortrekkers who packed up and rolled into the South African interior. The word goes back to Dutch trekken, 'to pull, draw, march,' the same tugging sense that drags a draught animal forward. English borrowed it in the 1800s for any arduous overland slog, and the doubled-up 'trekking' came along for the verb.