Seamless tile
A texture whose edges match, so copies placed side by side show no join.
See it in Noise & texture. Turn on Seamless tiling and look at the tile preview.
In plain words
Games and websites often repeat one small picture to cover a big area. If the left edge does not match the right edge, a line shows at every join. A seamless tile is made so its edges continue into each other. Repeat it as many times as you like, and it looks like one surface. Noise tools can do this by wrapping the pattern round on itself.