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The term "sod" may be used to mean grass grown and cut specifically for the establishment of lawns. However, in British English and in Irish English such material is more usually known as turf, and the word "sod" is limited mainly to agricultural senses (for example for turf when ploughed), or avoided altogether, due to the alternative offensive meaning of the word "sod".

Grass seed may be blown about by the wind, eaten by birds, or fail because of drought. It takes some weeks to form a visually appealing lawn and further time before it is robust enough for use. Turf largely avoids these problems, and with proper care, newly laid sod is usually fully functional within 30 days of installation and its root system is comparable to that of a seeding lawn two or three years older. However, turf is more expensive and requires considerably more water for its establishment. Erosion after seeding may be a concern in some areas near water. Sod reduces erosion by stabilizing the soil in these type of areas.

Source: Wikipedia

Sod roofs are typical of the Faroe Islands. Traditionally the roof is covered with sod on top of several layers of birch bark over gently sloping wooden roof boards. However, modern turf roofs often use a type of commercial roofing felt underneath the sod. Sod is also an effective insulator in a cold climate. Typically, a sod roof will last about 10 or more years before it has to be replaced. Some residents actually mow their roofs to keep them looking good.