Rope Dart isn't a real Magic: The Gathering keyword or ability—it doesn't exist in any official set, the Comprehensive Rules, or the keyword glossary. You may be thinking of a similarly named mechanic, or it could be a term from another game entirely (it's a real-world flexible weapon and appears in various video games).
If you encountered "Rope Dart" on a card or proxy, it's likely a custom/homebrew card, a joke card, or a misremembered name. Real keywords that involve reaching out or pulling effects include things like Reach (blocking flyers) or abilities that "tap target creature" or move things around the battlefield.
For an accurate explanation, double-check the exact card name or text. If you tell me the real keyword you're curious about, I'll break down what it does, the common rules misunderstanding, and why it matters in Commander.