The term arises from the union of the words Fake and Instagram, that is, a fake Instagram that users use, privately with a few friends and under a pseudonym, to share more 'real' photographs, without retouching or with a tone humorous.
This account, also called 'Finsta', is created in parallel to a public Instagram account in which it is published with a real name and whose content shows more aesthetic and aspirational images.
Other names:
Fake Instagram, fake Instagram