Chocolate and Dark chocolate

Chocolate noun - A food made from roasted ground cacao beans.

Dark chocolate and chocolate are semantically related. In some cases you can replace phrase "Dark chocolate" with "Chocolate", this terms are similar.

Dark chocolate noun - Chocolate liquor with cocoa butter and small amounts of sugar and vanilla; lecithin is usually added.

Chocolate and dark chocolate are semantically related. You can use "Chocolate" instead a noun phrase "Dark chocolate".