Unusual options activity

Also called Unusual flow, unusual volume, size over open interest

A flow larger than the contract's open interest, so at least part of it opened new positions.

A trade can only close as many contracts as are open. When a single flow is bigger than the contract's open interest, at least part of it has to be new positions. That's what Theta Vantage marks Unusual.

unusual = open interest > 0 and size > open interest

A flow whose open interest isn't known is never marked unusual, and the table says its open interest is unknown.

Reading it

New positions in size are worth a look, especially in short-dated, out-of-the-money contracts. They still don't tell you the intent behind them, and open interest is as of the previous close, so a contract that has traded heavily all day can look unusual on a trade that's partly closing.

In Theta Vantage

The outlined Unusual tag in the options flow table, the Unusual only filter, and part of what makes a golden sweep.