What is the term for the portion of the target that is struck by electrons?

The term "focal spot" refers to the specific area on the target within the X-ray tube where the high-speed electrons collide and produce X-rays. This spot is critical in radiography because it influences image quality; a smaller focal spot leads to sharper images due to less geometric blur, while a larger focal spot may cause images to be less distinct. The focal spot is essential for determining the degree of detail visible in radiographic images, thus making it a fundamental concept in dental radiography.

In contrast, "photon point," "principal point," and "end point" are not terms typically associated with the process or components of X-ray production. They do not accurately describe the interaction between electrons and the target in the X-ray tube, reinforcing why "focal spot" is the correct answer in this context.