The term 'Groundskeeper's Supply' refers to the materials and equipment used by a groundskeeper, which is a person responsible for maintaining the grounds of a property. The three-letter solution for this term is SOD, which stands for SOD, which is a type of grass turf that is often used in landscaping. SOD is typically sold in large rolls and can be used to cover large areas quickly and easily. Groundskeepers use SOD to create lawns, gardens, and other outdoor spaces.