Rotation, etc. of images is known more generally as data augmentation and you're correct in that it's a way to reduce amount of training data to cold start a data product.
For "synthetic data", my understanding is that it's referring to use of ML to generate brand new training samples (e.g. through GANs, though there are limitations [1]).
For "synthetic data", my understanding is that it's referring to use of ML to generate brand new training samples (e.g. through GANs, though there are limitations [1]).
1 - https://openreview.net/forum?id=rJMw747l_4