And there are only 2 "seasons": Summer (Bull) and Winter (Bear).
Someone might disagree with me as there are no real definitions to my knowledge to these terms. They are just memes from long time ago
True, as far as I know there are only the bull and the bear markets, which are the only seasons available on this environment. They are always ignited by a major movement in Bitcoin's price. If BTC goes up, we enter a bullish season and if Bitcoin goes down we enter a bearish season.
Altcoins don't have any influence on this process. It's quite the opposite, they are heavily influenced by the process.
I think what OP says about altcoin, memecoin, NFT seasons could be replaced by altcoin, memecoin, NFT hypes, what is also a consequence of the seasons, but not the seasons themselves.
I would say that it is a combined effort and not just bitcoin. I know everyone thinks that bitcoin going up means alts going up as well, but sometimes alts do matter in the process as well.
Luna crashing made bitcoin fall too, or FTX crashing made bitcoin fall too (albeit there was btc in that case too) so I would say that if there is alts that go down, we saw bitcoin go down as well and I am sure the opposite is true. I am not saying alts make bitcoin move, I am just saying that it is an overall thing and I believe that it should be a bit worrisome to never look at alts when you are looking for seasons. If it is alt season that means bitcoin had something to do with it, but if btc went up, then alts had something to do with that too.