Block trade
A large options trade negotiated off screen. US-listed option blocks still execute on an exchange as a single print, and size thresholds vary by scanner.
Block trades are usually negotiated between institutions or through a broker’s desk instead of being filled piece by piece on screen. For US-listed options the agreed trade is still executed on an exchange, so it reaches the tape as a single print. Because the price is agreed in advance, a block often prints near the midpoint of the quote, which gives less directional evidence than an aggressive trade at the ask or the bid.
Each scanner sets its own size threshold, so a print labeled a block on one platform may carry no label on another. A block can open a position, close one, roll an existing position or hedge stock.
Illustrative example (hypothetical numbers, not a real trade): 2,500 puts print as one trade at $3.40 while the quote is $3.30 bid and $3.50 ask. The premium is 2,500 × $3.40 × 100 = $850,000, and the midpoint price makes buyer and seller equally plausible as the initiator.