The tendency of earlier choices to constrain later ones, so that institutions or technologies persist even when better alternatives exist, because switching is costly or because beneficiaries defend the status quo.
In more detail
Douglass North (1990) argued that institutional change is incremental and path-dependent: organisations created under existing rules invest in them, informal norms adapt to them, and increasing returns make reversal costly. Examples include the QWERTY keyboard, legal traditions and electoral systems. Critics argue that the concept is used loosely and that many supposedly locked-in outcomes were in fact efficient or were reversed when conditions changed.