Rain lily (Zephyranthes).
Rain lily bulbs come in various shades of white, yellow, pink and rose. They are called rain lilies as they have a tendancy to bust into flower after rain in Summer/Autumn. In cultivation the rain lily will flower throughout the year if kept alternatively wet and dry with the majority of blooms in Summer and Autumn.
If you want more information about this flower, just search the plant's Latin (botanical) name on Google: