'Great Trek' definitions:

Definition of 'Great Trek'

From: GCIDE

Trek \Trek\, n. [Written also treck.] [D. Cf. Track, n.] The act of trekking; a drawing or a traveling; a journey; a migration. [Chiefly South Africa]
To the north a trek was projected, and some years later was nearly carried out, for the occupation of the Mashonaland. --James Bryce.
Great Trek, the great emigration of Boers from Cape Colony which began in 1836, and resulted in the founding of the South African Republic and Orange Free State. [Webster 1913 Suppl.]