Definition - What does Photobomb mean?
Techopedia explains Photobomb
The ability to share successful hijackings through social media has made photobombing an Internet meme. The range of photobombing techniques has expanded as social sharing has introduced variations. The most common photobomb is usually a form of photo lurking where a photobomber mugs for the camera in a shot he or she isn’t supposed to be part of (wedding photos, tourist photos and so on). More elaborate background setups include looking threatening and/or brandishing a weapon, mooning or flashing the camera, appearing in costume and so on.