A roach is the remains of a joint, blunt or roll up cigarette after most of it has been smoked. In Europe, the UK and most Commonwealth nations, the term is often used more specifically to refer to a short tube, commonly torn from a pack of rolling papers, that may be present in the unlit end of a joint.This hollow mouthpiece, customarily made of thin cardboard, is termed a "filter" in North America. It is commonly set in position during the rolling process, or may be inserted later. When the use of a roach is employed, a joint can still be held securely after it has burnt down to a short length; thus, the entire length of the joint may be smoked, without the aid of a roach clip.
In Spanish, tabaco de cucaracha refers to powdery, low-quality tobacco.