A sufficiency is an adequate amount of something. Before a winter storm, you should probably make sure you have a sufficiency of food stored in your house.
The noun sufficiency means the quality of being enough, adequate, or sufficient. Due to financial constraints, your local school district may be willing to settle for educational sufficiency, but hopefully you will hold the district to a higher standard than offering merely an adequate education to students. The opposite of sufficiency is insufficiency, meaning an inadequate amount. Of the two, you will likely hear insufficiency more often than sufficiency in conversation.