title: Kubernetes Secrets - What is the purpose of type "Opaque" in secret definitions
body: <p>In most examples about using secrets in Kubernetes, you can find similar examples:</p>
  
  <pre><code>apiVersion: v1
  kind: Secret
  metadata:
    name: mysecret
  type: Opaque
  data:
    username: User
    password: **********
  </code></pre>
  
  <p>What is the purpose of <code>type: Opaque</code> in the definition above? What other types (and for which use cases) are possible to specify there?</p>