What does "sparse" mean in the context of neural nets?
<p>I've seen "sparse" and "sparsity" used in a way that suggests it's something that improves a model's accuracy. For example:</p>

<blockquote>
  <p>I think the unsupervised phase might be not so important if some
  sparse connections or neurons are used, such as rectifier units or
  convolutional connection, and big training data is available.</p>
</blockquote>

<p>From <a href="https://www.quora.com/When-does-unsupervised-pre-training-improve-classification-accuracy-for-a-deep-neural-network-When-does-it-not" rel="noreferrer">https://www.quora.com/When-does-unsupervised-pre-training-improve-classification-accuracy-for-a-deep-neural-network-When-does-it-not</a></p>

<p>What does "sparse" mean in this context?</p>