A topmast is the second section of a tall ship's mast, the vertical pole that holds up the sails. On large sailing ships, the mast wasn't one continuous pole: it was built in sections stacked on top of each other, like segments of a telescope. The lowest section, rising from the deck, was called the lower mast. The topmast fit into the top of the lower mast, extending the height significantly.

Why build masts in sections instead of using one tall pole? Partly because finding a single tree tall and strong enough was nearly impossible. But sailors also needed flexibility: if a storm damaged the topmast, they could replace just that section without replacing the entire mast. During severe weather, crews could even lower the topmast to make the ship more stable.

The topmast carried important sails called topsails, which caught wind high above the deck where it blew stronger and steadier. On the largest ships, there might even be a third section above the topmast, called the topgallant mast. Working on the topmast meant climbing high above the deck on rope ladders called ratlines, then standing on narrow footropes while adjusting the sails, dangerous work that required courage, balance, and skill.