Final answer:
The correct term for the impression or pattern seen when holding paper up to the light is called a watermark. It serves as a security feature to prevent forgery.
Step-by-step explanation:
The impression or pattern that can be seen when paper is held up to the light is called a watermark. Option a) Watermark is the correct answer. Watermarks are created by making thicker and thinner lines in the paper when it is produced, which can be seen when the paper is held up to light. They are often used as a security feature in banknotes, passports, and other important documents to prevent forgery and to verify authenticity. Unlike embossment, seals, or transparency, a watermark is integrated into the paper itself and is not a surface treatment or a separate feature.