SYD stands for Sum of Years' Digits and is a function in Google Sheets used to calculate the depreciation of an asset. It takes four arguments:

Cost: The initial cost of the asset. Salvage: The value of the asset at the end of its useful life. Life: The useful life of the asset. Period: The period for which you want to calculate depreciation.

The SYD function uses a depreciation method that assumes that the asset will lose value more quickly in the earlier years of its useful life and more slowly in the later years. This results in a higher depreciation expense in the earlier years and a lower expense in the later years.