With most tile, the clay is stamped into square blanks then fired. In the firing process, the tile can remain square, or it might fire slightly out-of-square. Say 1/6th" off on this tile, 1/32nd on the next, etc. Or it might have a slight warp to it, along the line of a pringle potato chip. Or it can pillow a bit.

With the slight variations in size and shape from tile to tile, non-rectified tiles usually need a slightly wider grout line width, the wider grout line will absorb the size variations. If you tried to set them tight, the variations in size could kick your tile off the layout lines as you worked across the floor.

Rectified tile is fired in large sheets and cut to size after firing. So rectified tiles are normally quite square and flat. Being uniform in size, they can be set with a smaller grout line.

If a tile is "rectified" it'll almost always be described as such. Some non-rectified have chamfered edges, so "square edge" might just be more square than a chamfered edge.

With a chamfered edge, the eventual grout line can appear wider than the distance the tiles were set apart due to grout filling the chamfer.

Usually an email to the tile tech department will resolve any confusion over verbage used to describe the tile.