Any systems based on blockchain technology are blockchain platform? I read topic on the internet with list of blockchain platform but there is no bitcoin although bitcion based on blockchain. Can you clarify what is really blockchain platform is and how to differentiate them?
A 'system' or DApp you would say is a service or application running on a blockchain. Bitcoin being one of the more popular & well known applications of blockchain technology. Bitcoin was not the first or only service to use blockchain technology, however it is certainly one of the most well known.
Bitcoin has it's own Blockchain - think of this as a sort of public ledger. The majority of DApps or alt-coins will leverage the bitcoin blockchain due to it's major adoption & computation power etc. Think of it like an iPhone developer making his mobile app on Apple OS because he doesn't feel Blackberry is strong enough. You are using the one with the most social proof.
Now other DApps & alt coins might use other blockchains. For example you might use Ethereum blockchain as Ethereum has a different set of 'principles' & has it's setup differently in accordance with what it feels the community is searching for.
Hope this helps, feel free to ask if you need any clarity.