A straight stream can be defined as:

A straight stream is characterized as a solid column of water that is directed toward a target. This type of stream is advantageous in firefighting as it provides substantial reach and penetration, allowing for efficient application of water on the fire. The concentrated flow minimizes evaporation and maximizes the impact on the burning material, effectively cooling and extinguishing flames.

The other options describe different types of water patterns or streams. A wide-angle water pattern refers to a dispersed water spray that covers a broader area; it is less focused than a straight stream. An adjustable fog nozzle creates a pattern that can be modified, typically to produce a mist or fog effect for cooling and suppression, as opposed to the concentrated flow of a straight stream. A dropping cascade of water indicates a pattern where water falls downwards, which lacks the directed force that a straight stream provides. Each of these alternatives serves specific purposes in firefighting but does not encapsulate the focused and direct nature of a straight stream.