Definition in Human Design is about whether your fixed centres connect into one piece. Single definition means every defined centre is joined together — one block, with energy running from any centre to any other without a break. Around forty percent of people are built this way; it's the commonest kind.
Mechanically that means you process quickly and don't need anyone outside to complete the wiring. A split-definition person has to wait for a particular person or place to bridge two blocks before things flow; you don't — your inside is already through.
Where you'll recognise it: solitude is fine, decisions rarely need consultation, you often think a thing right through alone, and you often forget to bring anyone in. Running well, you're the most self-contained: steady, consistent, today's you much like yesterday's, and people who lean on you find you there. Stuck, you're closed — so self-sufficient you can't tell what perspective you're missing, or impatient with how long others take. The commonest single-definition mistake isn't thinking wrongly; it's not realising other people's wiring differs. What runs in one breath for you genuinely needs another person in the room for someone with a split.
