Abbreviation: DC = "Defocus-image Control" (Nikon)

The abbreviations means "Defocus-image Control"

Explanation from Nikon

AF DC-NIKKOR lenses feature exclusive Nikon Defocus-image Control technology. This allows photographers to control the degree of spherical aberration in the foreground or background by rotating the lensī DC ring. This will create a rounded out-of-focus blur that is ideal for portrait photography. No other lenses in the world offer this special technique.

See examples of effected products

Nikon AF 105mm f/2 D DC
Nikon AF 135mm f/2 DC