Keras is a high-level neural network API, written in Python and capable of running on top of TensorFlow, CNTK, or Theano. It was developed with the aim of enabling fast experimentation. 

Here are some of the key uses of Keras:

• Allows for easy and fast prototyping (through user-friendliness, modularity, and extensibility)
• Supports both convolutional networks and recurrent networks, as well as a combination of the two
• Runs seamlessly on CPU and GPU

Keras was designed on the following principles:

• User-friendliness
• Modularity
• Easy extensibility
• Compatibility with Python

To learn more about Keras, check out https://keras.io/.