Recurrent neural networks (RNN) can model sequential information. They do not assume that the data points are intensive. They perform the same task from the output of the previous data of a series of sequence data. This can also be thought of as memory. RNN cannot remember from longer sequences or time. It is unfolded during the training process, as shown in the following image:

Recurrent neural networks RNN

Recurrent neural networks RNN

As shown in the preceding figure, the step is unfolded and trained each time. During backpropagation, the gradients can vanish over time. To overcome this problem, Long short-term memory can be used to remember over a longer time period.