A crawler is something that moves slowly along the ground, usually on hands and knees or by dragging its body. Babies are crawlers before they learn to walk, scooting across the floor to reach their toys. Insects like caterpillars and beetles are crawlers too, inching along leaves and branches.

In technology, a crawler is a computer program that methodically explores the internet, moving from one webpage to another by following links. Search engines use crawlers (sometimes called spiders or web crawlers) to discover and catalog billions of webpages. These crawlers work tirelessly in the background, reading content and updating the search engine's massive index so you can find what you're looking for in seconds. Just as a baby crawls from room to room exploring a house, a web crawler moves from page to page exploring the internet.

The word can also describe vehicles designed to move over rough terrain, like a tracked crawler used in construction, or a dungeon crawler video game where you explore maze-like underground spaces room by room.