What is the term used to describe the flipping of letters either horizontally or vertically?

The term that describes the flipping of letters either horizontally or vertically is indeed "inversions." In the context of reading and literacy, inversions typically refer to the phenomenon where letters like 'b' and 'd' or 'p' and 'q' are confused due to their mirrored shapes. This can be particularly common in young children as they are developing their literacy skills, and it reflects their ongoing understanding of letter forms and orientations. Recognizing and addressing inversions is important for educators as they support students in their reading development, helping to ensure that they can accurately identify and differentiate between letters as they become more proficient in reading and writing. This understanding is crucial in early literacy instruction, as it lays the groundwork for effective reading skills.