What type of joint is characterized by melting the materials together?

The correct choice is characterized by the process of melting materials together, which is specifically associated with a welded joint. A welded joint is created when two or more metal pieces are joined by applying heat to melt the edges of the materials so they can fuse together as they cool. This process creates a strong bond as the molten metal solidifies and forms a continuous structure.

In contrast, a sweat joint involves a different process where two metallic components are joined using a filler metal that is melted and then drawn into the joint by capillary action, but does not involve melting the base materials themselves like in welding. Other types of joints, such as compression or mechanical joints, rely on physical pressure or mechanical means to hold materials together rather than melting them. Thus, the welded joint is clearly the type that entails melting the materials to achieve a strong and lasting connection.