For anyone who has seen the Nicholas Roeg film, from 1971, that takes this word as its title, the definition is visual. You could watch that film with no sound and understand this word. Try it.
Or you might start with the OED definition and etymology which notes that this noun is of Australian origin but begins with a generic, modern catchall meaning and gives specifics on the origin second (after the jump; of particular value, see the last sentence of the 1979 reference):
1. A person who travels on foot, esp. for an extended period of time; a swagman or traveller.
2 a. Austral. Journeying undertaken on foot into the bush by an Aborigine who wishes to live in a traditional manner for a period; an instance of this.
1897 W. E. Roth Ethnol. Stud. N.-W.-Central Queensland Aborigines ix. 132 The ‘Walk-about’ is perhaps‥one of the most important institutions in vogue among the aboriginals, and yet one on account of which their white brethren will, as often as not, hold them up to ridicule and contempt. To the settlers it is considered in the light of an excuse for a holiday or for shirking the work upon which the blacks would otherwise be employed.
1898 K. Langloh Parker More Austral. Legendary Tales p. ix, Should the local tribes know nothing of what I wanted to hear, I would get them to make enquiries of wandering Blacks from other tribes whom they might meet during their periodic ‘walk-abouts’.
1979 New S. Wales Parl. Papers (1980–1) 3rd Sess. IV. 598 White people think walkabout is going for a walk into the bush and lying in the sun and doing a bit of fishing. Walkabout the Aboriginal way is where a man or a woman goes out to a sacred place. As you go to a cathedral the Aboriginal does this.
2003 B. Plotkin Soulcraft iv. 77 During his walkabout, the aboriginal youth wanders into the bush alone for several weeks or months, avoiding the company and conversation of other humans.