Skeletal muscle has got many many peripheral nuclei. What does "peripheral" mean here?
'Peripheral' in this context refers to the position of the nuclei within the skeletal muscle cell.  They are in the periphery (outer part) of the cell body rather than central as in most cell types.  More specifically, they are "subsarcolemmal", i.e. just under the sarcolemma, the cell membrane of the muscle fiber cell (source):



(Image from Wikipedia)

The many nuclei of a skeletal muscle cell are spaced out along the length of the cell (source 1, source 2).