Rust (the reddish-brown corrosion on metal), from the English word 'rust'. In everyday Japanese people usually say 'sabi', but 'ラスト' may appear in specialist or loanword contexts.
古い自転車のフレームにラストが広がっていたので、修理に出した。
Rust had spread across the frame of the old bicycle, so I took it in for repair.
海辺の設備は塩害でラストが発生しやすいので、定期的な点検が必要だ。
Coastal facilities are prone to rust from salt damage, so regular inspections are necessary.