A question regarding definition of Pareto efficiency
the process of moving from one point to another i.e. reallocation makes one person better off while making another person worse off. for instance, moving from the lower part of the contract curve to a higher part makes Octavio better off as Octavio's indifference curve goes further away from the origin. However, the process makes Abby worse off as Abby's indifference curve moves closer to the origin.

There exist multiple points of pareto efficient outcomes which are stable, i.e. no more trading occurs.