1. What is a seamless texture/ tileable texture
To put it simply, a seamless texture is an image that can be repeated as many times as needed without any breaks or obvious seams, each corner of the image must be able to meet up and match perfectly with the other.
Some examples of seamless texture：
Examples of non-seamless Texture:
2. Why do we need a seamless texture
Some designers will search textures they want to show in their design project online and find that the rendering appears with weird material, that is because the image they use in the model/finish is not a seamless one. In order to keep the products to be realistic in the renderings, you will need to use some software like Adobe Photoshop to make seamless textures.
Rendering effect of using non-seamless texture / Rendering effect of using seamless texture