Could someone tell me what material this pipe is? It has a tiny leak that I taped up until I fix(02)

Could someone tell me what material this pipe is? It has a tiny leak that I taped up until I fix(02)

Image gallery: Tiny Leak

Why Small Leaks Could Lead to Larger Plumbing Problems How to fix tiny leak from faucet stem? : Plumbing Could someone tell me what material this pipe is? It has a tiny leak that I taped up until I fix