Spark plug

A spark plug comprising:

• a ground electrode and
• a center electrode
• wherein at least one of the ground electrode and the center electrode, as a first electrode, includes:
• an electrode body
• an electrode tip layered with the electrode body in a layering direction;
• and
• a weld part formed between the electrode body and the electrode tip;
• the weld part has an orthogonal projection on a virtual plane perpendicular to the layering direction, wherein the orthogonal projection includes a plurality of projecting portions extending in a specific direction and being arranged in a direction perpendicular to the specific direction, wherein each of the plurality of projecting portions includes a peak in the specific direction;
• the weld part satisfies a mathematical expression of B>A, where A represents a length of a first line segment, and B represents a length of a second line segment;
• the first line segment is a virtual line segment connecting the peak of a first one of the plurality of projecting portions to the peak of a second one of the plurality of projecting portions adjacent to the first projecting portion;
• and
• the second line segment is a virtual line segment that is perpendicular to the first line segment and connects the first line segment to a point of an outer periphery of the weld part, wherein the point is farthest from the first line segment in a section between the peaks of the first and second projecting portions facing the first line segment.