By Robinhood's reckoning, half of all brokerage accounts opened in America since 2015 have been set up on its platform.

据Robinhood估计，2015年以来在美国开设的所有经纪账户中，有一半是通过其平台开设的。

Maybe that's a 401 or a Roth IRA or a brokerage account.

也许这是 401 账户、Roth IRA 账户或经纪账户。