The seed-bearing cone of a pine tree. The word is a compound of 松 (pine) and ぼっくり (a mimetic word for something round and lumpy).
See also: 松かさ
I picked up a big pinecone in the park.
松ぼっくりは乾燥すると開く。
Pinecones open when they dry.
Very rare kanji form; 陰嚢 means 'scrotum', reflecting a humorous or old-fashioned name for pinecone.