Tachash (תַּחַשׁ) means fine leather, probably porpoise or seal skin — a durable, weather-resistant material. The exact animal is debated (dugong, dolphin, or fine-grained leather). Used for the tabernacle's outer covering.
Exodus 26:14: 'Make for the tent a covering of ram skins dyed red, and over that a covering of fine leather.' Numbers 4:6: the ark of the covenant was covered with tachash during transport. Ezekiel 16:10: God says to Jerusalem, 'I put sandals of fine leather on you.' The finest materials were used for God's dwelling — nothing cheap or second-rate for the place where heaven met earth. This challenges us: do we give God our best, or our leftovers?