html tag what does the ogg mean code example

Example 1: how do you play audio files on html

<audio src="sound.mp3" autoplay></audio>

Example 2: html video tag

<video width="320" height="240" controls>
  <source src="movie.mp4" type="video/mp4">
  <source src="movie.ogg" type="video/ogg">
  Your browser does not support the video tag.
</video>