Today it means: A selection effect driving evolution of an invasive species at the invasion front, that selects the fastest and furthest invaders to interbreed creating stronger and faster invaders, due to the invasion front preselecting the fastest invaders, concentrating these individuals and therefore selecting those traits that let them invade faster. Full definition →
From Olympic village + effect. From the breeding population selection effect resulting in a group of superior performant individuals like found at an Olympic village (the sportspeople housing for the Olympics).
Etymology from Wiktionary, CC BY-SA 4.0.