The meaning of "multimedia" is "digitally-unified media".
In particular, multimedia teaching/learning-materials mean digitally-unified teaching/learning-materials. They are digital documents.
Making multimedia materials as digital documents, compared to publishing printed matters, has following merits:
One can complete the whole process by oneself.
Low cost, high quality.
We can make a comfortably spacy document.
In the case of printed matter, space is money. This does not hold for digital document.