An "indelible" mark is one that is:

An "indelible" mark refers to something that is permanent and cannot be easily removed or erased. The term is often used to describe things like ink stains or tattoos because they leave a lasting impression. This permanence is intrinsic to the meaning of the word "indelible," which comes from the Latin root meaning "cannot be wiped out."

The other choices describe marks that do not align with the idea of permanence. A mark that is temporary and easily erased implies it can be wiped away, while faint and hard-to-see suggests it may not even be noticeable, both of which contradict the lasting nature associated with indelible marks. An occasionally visible mark, similarly, implies that it may disappear at times, which also does not fit the definition of something that is permanent. Therefore, the option indicating permanence accurately captures the essence of what an indelible mark is.