"75%" is a community term for an old design. The 75% layout design principle is a keyboard with the function key row present, and only one column of keys to the right of backspace and enter:
This design achieves a reduction of space almost as great as a 60% keyboard, but retains comparative ease of access to the navigation keys as well as to the function keys. 75% layouts are widely used on laptops. The top row may use smaller keys, to save space or to fit in an extra key into the row; alternatively, F11 and F12 may be moved into the Fn layer.
"75%" is not a standard layout, and the precise arrangement of keys varies between products.