What is a tessellated image?

Tessellated image can be one of two things 1 a repeating pattern, wether it be a bunch of blue squares or more complex shapes Or 2 what happens when a grid is displayed on a screen too low resolution to display it (happens all the time on my 1080p monitor) it's like if you look at a brick wall then woomera out on the pc, those lines that appear are tesselations