Accumulated depreciation of a particular plant asset refers to: half-yearly depreciation total depreciation. or neither?

Accumulated depreciation of a particular plant asset refers to neither the half-yearly depreciation nor total depreciation.

Accumulated depreciation is the total depreciation expense reported since the plant asset was bought. Its amount is used to determine the book value or carrying value of the plant asset. 

When the plant asset is fully depreciated, that is only the time when accumulated depreciation is equal to the total depreciation.