What is "to dress to the left"

Dress \Dress\, v. i.

1. (Mil.) To arrange one's self in due position in a line of soldiers; -- the word of command to form alignment in ranks; as, Dress right, dress!

2. To clothe or apparel one's self; to put on one's garments; to pay particular regard to dress; as, to dress quickly. ``To dress for a ball.''
   --Latham.

   To flaunt, to dress, to dance, to thrum.
   --Tennyson .

   To dress to the right, To dress to the left, To dress on the center (Mil.), to form alignment with reference to the soldier on the extreme right, or in the center, of the rank, who serves as a guide.