A very simple definition, from the pages of Chesteron’s newspaper K’s Weekly:
There are many readers of this Paper who are not members of the League. All who believe that ownership in the means of livelihood is normal to man, and necessary to liberty, and all who dislike and distrust the concentration of control advocated by Socialists and practiced by Monopolists, should join the League. There is no other tenet for membership, and no other obligation…although active work is welcomed from all who can give it.
Elsewhere on the page, one could find this sidebar:
THE LEAGUE offers the only practical alternative to the twin evils of Capitalism and Socialism. It is equally opposed to both; they both result in the concentration of property and power in a few hands to the enslavement of the majority.