Whereupon means immediately after which, or as a direct result of which. It connects two events to show that the second happened right after the first, often as a consequence.

When you read that “the magician pulled a rabbit from his hat, whereupon the audience burst into applause,” it means the applause happened immediately because of what the magician did. The word signals a quick cause and effect.

You'll mostly find whereupon in stories and formal writing rather than everyday conversation. A friend wouldn't say “I finished my homework, whereupon I went outside to play.” They'd just say “then I went outside.” But in a book, you might read: “The knight defeated the dragon, whereupon the grateful villagers threw a great feast in his honor.”

The word helps writers show tight connections between events. “The scientist completed her experiment, whereupon she discovered something remarkable” emphasizes that the discovery happened right then, as a direct result of finishing the work. It's like saying “and then, because of that” but in a single, elegant word. When you see whereupon in your reading, pay attention: something important just happened, and something else important is happening because of it.