This article serves as a basic definition of the corresponding keyword on the site socioeco.org.
Ecological debt refers to the debt that some countries (usually of the North), companies or actors have towards other countries (usually from the South), companies or other actors.
The Eco Debt means calling in the historical debt that the industrialized countries from the North have with the Third World for the intellectual, historical and current appropriation of ancestral knowledge. The primary knowledge, illegally and illegitimately appropriated, relates to seed improvement, the use of medicinal plants and other know-how that form the base of today’s biotechnological and agroindustry and for which the countries from the South now have to pay royalties.
On a less anthrocentric basis ecological debt describes the consumption of resources from within an ecosystem that exceeds the system's regenerative capacity. See the WIkipedia definition for this acception.