An arcuate delta is one that's shaped like a triangle. It forms when a river meets a sea with alternating current directions. The Nile delta is an example of an arcuate delta.
A cuspate delta is one that's vaguely shaped like a letter V with curved sides. It forms when a river flows into a sea with waves that hit it head on, spreading the deposited sediment out. The delta of the Ebro river in Spain is an example of a cuspate delta.
A bird's foot delta forms when the river's current is stronger than the waves of the sea. The river carves out channels into the sea, spreading out like a bird's foot. They are quite rare; the best–known example is the Mississippi delta.
For more information, including photographs, try the Geography AS Notes website (to which I am indebted for all of this information).
© Haydn Thompson 2017