“16-lines” refers to a multi-line / 4D / 4×360° (or multi-plane) laser level: typically, the device emits multiple laser beams / planes — often horizontal and vertical — simultaneously, and may project them around the entire room or site (360°) in multiple directions.
These multiple lines allow you to get full-room or full-site reference grids: floor to ceiling, side to side, across walls, for corners, layout lines, structure alignment etc. That’s far more powerful than a simple single-line or two-line (cross) laser.