실고추 (shil-gochu) is dried red peppers shredded or sliced finely into threads. 실 (shil) means ‘thread’ or ‘string’ and 고추 (gochu) means red pepper. I’ve also seen it spelled in English as sil kochu.

This is the Wang brand I found at the Korean supermarket California Market. The label has French on it — piment. The rest of the information on the plastic packaging:

깨끗한 우리 간산에서 자란 자연의 선물! 원료명: 고추

NUTRITIONAL FACTS
Serving size: 1 gram
20 servings per container
No calories, fat, cholesterol, sodium, carbohydrates or protein!
No vitamin A, calcium or iron.
4% Vitamin C based on 2,000-calorie diet.

Product of Korea. 한국산. ITEM NO. 00655. UPC 0 87703 00203

DISTRIBUTED BY WANG GLOBALNET. Vernon, CA 90058. San Leandro CA 94577-5706. Brooklyn , NY 11206. Houston, TX 77036. Chicago, IL 60640. Columbia, Maryland 21045. Suwanee, Georgia 30024. Dallas, TX 75229. Kent, WA 98032

KOHA ORIENTAL FOODS. Honolulu, Hawaii 96817. PAN ASIA FOOD CO., LTD. 435 Ambassador Drive, Mississauga, Ontario, L57 2J3. Wang Glboalnet Trading BC Ltd. 622 Chester Road, Delta, BC, Canada V3M 5V8.
Shinmi Australia Pty. Ltd. 46 Sarratt St North, Silverwater NSW 228. Asian Savour World Pty. Ltd. 503 Mt Wellington Highway Auckland New Zealand.

Shilgochu is used as a garnish for Korean dishes.