The cyanogenic glucoside in cassava that can release hydrogen cyanide if poorly processed is linamarin.
Linamarin is concentrated in cassava roots, leaves, and peels, and is also found in plants such as lima beans and flax. In damaged cassava tissue, the plant enzyme linamarase breaks linamarin down, producing cyanide-containing compounds that can release hydrogen cyanide.
This is why cassava is not simply peeled and eaten raw. Traditional preparation methods include soaking, fermenting, drying, boiling, grating, and roasting. Bitter cassava generally contains more cyanogenic compounds than sweet varieties, and inadequate processing has been linked to acute cyanide poisoning and the neurological disease konzo.
A common mix-up is confusing linamarin with hydrogen cyanide itself. Linamarin is the plant compound or precursor; hydrogen cyanide is the poisonous chemical released during enzymatic breakdown. Lotaustralin is a related cyanogenic glucoside also present in cassava, but linamarin is the canonical answer to this question.