Final answer:
An iris-in or iris-out is a vintage editing technique involving the gradual contraction or expansion of a circle to transition between scenes. The most accurate choice from the given options would be 'd. Dissolve,' though it doesn't perfectly describe the uniqueness of the iris technique.
Step-by-step explanation:
An iris-in or iris-out is a technique of editing that resembles the opening or closing of an iris. When an iris-in is used, the screen transitions from black, opening to reveal the scene. Conversely, an iris-out transitions from the scene closing down to black. This editing technique was commonly used in silent films and early talkies to focus attention on a particular part of the scene or to indicate the beginning or end of a scene.
The correct answer to the question, "Which aspect or technique of editing is an iris-in or iris-out?" is d. Dissolve. However, while it resembles a dissolve in that it represents a gradual transition, because an iris specifically involves a circular contraction or expansion, it could also be considered unique enough not to fit neatly into these categories.