Water precipitation in the form of clumps of small ice crystals.
Snow is water precipitation in the form of "fluffy" clumps of small ice crystals. Contrast with sheet ice and hail where the ice freezes into a solid sheet or block, respectively.
Snow is often better for plants than solid ice. This is partly because it can form thermal insulation protecting the plants from the worst of the cold, but also snow tends to only form at intermediate temperatures. Although counter-intuitive, the saying "too cold for snow" has some truth to it.
However, care should still be taken for many plant varieties. As well as cold, snow can add a significant weight to the branches of plants - causing physical damage.
Use this tag for all questions about handling snow in a garden: how to protect plants, etc.