The Northwest Corner Rule is a method used in the transportation problem to find an initial basic feasible solution. It starts at the top-left (northwest) corner of the transportation tableau, allocating as much as possible to that cell without exceeding the supply or demand constraints. After making an allocation, the algorithm moves either down to the next row or right to the next column, depending on whether the supply or demand has been satisfied, and continues this process until all supplies and demands are met. This rule provides a straightforward and systematic way to generate an initial solution for optimization.