I've heard of Instagram before, but it's not something I'd use in relation to social media. When I think of Instagram, I think of people just posting pictures and video snippets of their lives.
Instagram's name derives from the word 'instant', as in how old cameras were marketed as 'instant', which is something the creators felt taken for granted. They also used the word 'gram' in relation to 'telegram' as they felt the snapshots individuals took of their lives were some kind of telegram. When joined, they created 'Instagram'. Got to admit, that's a pretty interesting fact!

Affordances and Limitations
The 'selfie' as a function, can be viewed as a means of self-expression, a construction of a positive image or self-promotion. It can also be used as a cry for attention or love, or a way of belonging to the community. The 'selfie' make up most of the images that are put in Instagram. By expressing themselves through a selfie, an individual, Instagram users, construct their identities and express their belonging in the community.

Revenue Model:

There are various tools used in Instagram that are used a revenue model. For example:
Explore Tab: Which creates an opportunity for brands to use the promoted feature, an it's an explore tab in which featured photos (paid) are shown.
Filters: Instagram as photo filters that users can apply to their image, and companies that which to promote their brand usually pay a free in order to advertise their image.
Video: Instagram used to be a photo-sharing app, until they allowed the users to add in videos up to 1 minute. Like images, companies use videos to promote their services and products.