ice floe

Short definition from Wiktionary

Noun

1. 1
   Any type of sea ice not attached to land, drift ice.
2. 2
   An ice dam (ice jam), a blockage of ice in a river starting with an ice floe in the river.
3. 3
   An ice stream (ice flow), a type of fast moving glacier
4. 4
   A flat mass of floating ice, smaller than an ice field.