The first time digital interfaces came into existence, designs were quite basic. Straight lines, simple shapes and text. But soon after that, with higher resolution displays and faster GPUs the possibilities became endless.
The earliest designs in digital GUIs resembled a much of real world objects. Skeuomorphic design aims to emulate the aesthetics of physical design. This type of design was very common in the early designs at Apple. That eventually changed to a more digital-first design, also known as the flat design.
Skeuomorphic design is common in digital plugins in the audio production domain. Knobs and meters resemble the actual physical instrument.