In the following article, Erika Mulvenna explains the difference between a cross-wound or stacked wound spool of thread.

"Most spools of thread are wound one of two ways, cross-wound or stacked. The red and blue spools on the left in the picture above are cross-wound spools. The thread has been wound on the spool in a criss-cross way, resulting in a pattern of “X’s” on the spool. The green and gold spools on the right in the picture above are stacked. The thread has been wound on the spool to stack one row above the other, resulting in a pattern of straight lines on the spool.

Cross-wound spools work best on a horizontal spool pin along with a foam pad and spool cap to help keep the thread from wrapping around the pin. Stacked spools work best on a vertical spool pin along with a foam pad to help keep the thread from wrapping around the pin."