A call option is characterized as being "American style." What does this mean?

American-style call options are distinct because they allow the holder the flexibility to exercise the option at any time prior to expiration. This characteristic stands out compared to European-style options, which can only be exercised on the expiration date itself.

The ability to exercise at any time gives the holder strategic advantages, especially if market conditions shift favorably. For instance, if the underlying asset sees a significant price increase, the holder can choose to exercise the option immediately to capture those gains, rather than waiting, which could result in missed opportunities.

Other options presented might refer to aspects of options trading but do not capture the essential feature that defines American-style options. Thus, the correct choice emphasizes the key feature: the right to exercise at any time before expiration.