From: https://en.m.wikipedia.org/wiki/Market_distortion

In the context of markets, “perfect competition” means:

1. - all participants have complete information,
2. - there are no entry or exit barriers to the market,
3. - there are no transaction costs or subsidies affecting the market,
4. - all firms have constant returns to scale, and
5. - all market participants are independent rational actors.

See also assume a can opener