Unity UI Tutorials - Sliced Image [03]
9-slicing is a 2D technique which allows you to reuse an image at various sizes without needing to prepare multiple Assets. It involves splitting the image into nine portions, so that when you re-size the Sprite, the different portions scale or tile (that is, repeat in a grid formation) in different ways to keep the Sprite in proportion. This is useful when creating patterns or Textures, such as walls or floors in a 2D environment.
https://docs.unity3d.com/Manual/9Slic...