Which term describes a closed sac or pouch containing fluid semisolid material?

The term that describes a closed sac or pouch containing fluid or semisolid material is "cyst". A cyst is an abnormal growth that can occur in various parts of the body and vary in size and content. Cysts can be benign (non-cancerous) or malignant (cancerous). Depending on their location and nature, cysts can cause symptoms and may require medical treatment or management.