What is water in its solid form called?

Water in its solid form is called ice.

At ordinary atmospheric pressure, water freezes at 0 °C (32 °F or 273.15 K). As it solidifies, hydrogen bonds arrange the water molecules into an orderly crystal structure. The most common natural form is hexagonal ice, known scientifically as ice Iᵧ.

Ice has an unusual property: it is less dense than liquid water, so it floats. Freezing expands fresh water by about 9%, which explains why ice can crack rocks, burst pipes, and damage roads. Floating ice also forms an insulating layer that helps aquatic life survive beneath frozen ponds and lakes.

“Ice” is the everyday and canonical answer, although scientists recognize many less-common solid phases of water that form under extreme pressure or temperature. Snow, hail, frost, glaciers, and sea ice are all forms or accumulations of ice. A common mix-up is confusing ice with snow: snow consists of ice crystals that fall from clouds, while ice is the broader solid form of water.