Is Indie a game genre?

The only place that I see that Indie is a genre is on Steam, and my teacher tells me that Indie isn't a genre of games.

What do you think? Can we say that Indie is a genre?

Indie (comes from independent) is not per se a genre, but a paradigm of producing and publishing (here, games).

Indie game companies are mostly small and therefore more flexible, and open to new and crazy ideas than larger companies like Activision/Blizzard or Ubisoft, which concentrate on marketing one big product to a large number of customers.

An indie game is no different than non-indie games, but might have a larger scope in terms of genres. Some are indeed not in any genre one can categorize easily.

Indie isn't a genre in the strictest sense. It's more of a subculture of games, which can then be classified in genres. There are indie RPGs, indie arcade games, et cetera.

The term comes from music, where indie pop and indie rock are actual genres. (Sub-genres?)

Indie can definitely be considered a category of games, the same way independent films are. Similarly, these are low-budget or even no-budget productions undertaken by a small group of people with very limited funds, many of whom may do it for the fun of it rather than in the hope of striking it big.

Having said that, it's hard to see where to draw the line, since most game studios start out being 'indie' before becoming successful.

No, "Indie" is not a genre. "Indie" merely refers to the production of the game. You can have Indie puzzlers, platformers, shooter, racers, etc. These are genres.