Inclusions are defined as:

Inclusions are defined as foreign solid matter that becomes trapped within the weld. This can occur when materials such as oxides, slag, or other debris are unable to escape the molten weld pool during the welding process. The presence of inclusions can significantly weaken the integrity of the weld, leading to issues such as reduced structural strength or failure under stress.

This definition highlights the importance of cleanliness and proper technique in welding to minimize the risk of such defects. Inclusions differ from the other options, which describe other phenomena related to the welding process, but do not accurately define what inclusions are. For instance, metal particles sprayed out during welding refers to spatter, while pieces of rod or metal used as filler define filler material rather than inclusions. Gas pockets trapped in the weld, known as porosity, are also a separate issue that affects weld quality but is not related to the definition of inclusions.