Job roles which are not fully defined in advance, and which evolve over time through a process of negotiated joining (which is also how hiring into open-ended roles is done).
Open-endedness allows the roles in teams and organizations to continually change and adapt as the situation changes, making them more resilient and adaptable. Negotiated joining also produces teams that are tighter-knit and more effective at the work of uncertainty (which includes innovation). Simply put, open-ended roles are more appropriate for uncertainty than conventional, stable, fully defined roles.
See also: amorphous organization, diversity, strategy, uncertainty mindset, voluntary uncertainty.