Event CG

Event CGs (often just referred to as CGs) are full-screen images that represent a particular moment in a scene that can’t generally be represented using the character sprites or even a special one-off sprite and are often used as rewards for the player. CGs may have multiple variations (ex: before kiss/during kiss, day/night, outfit A/outfit B; etc) or light animation (ex: blinking, hair moving, dust motes; etc) but are generally a single static image. Usually, CGs are reserved for special events that are intended to highlight the importance of a moment or for a special scene and almost always include a (frequently detailed) background.

Cut-ins

Cut-ins are small graphic elements that are introduced onto the screen, usually overlaying what was already there (and "cutting in" to the scene). Examples: items that characters are looking at/picked up, an off-screen character's reaction shot, a close-up detail of a CG or background, an action-pose character sprite with custom frame or special effect.