The three letters “G,” “I” and “F.” Together, they represent an image format, but there is some controversy over how it's pronounced.
Tom Scott [1] presents the arguments for the two ways GIF (Graphics Interchange File) is pronounced, but I like Mike Rugnetta's take [2] which is a completely different pronounciation based on “ghoti” (the alternate spelling for “fish”).
[1] https://www.youtube.com/watch?v=N1AL2EMvVy0