This is a single spool of smoke (gray) monofilament ice fishing line.  It is available in 1, 2, or 4 # test.  Product Specs:

Micro-Mono is a great monofilament ice fishing line:

• Invisible in water, but highly visible against ice/snow
• Micro thin, dark gray monofilament
• Ideal for ice fisherman seeking a fine diameter, sensitive line that detects the  most delicate nudge or bump under the ice