Alto in Portuguese has a few meanings that you are sure to come across, the most basic of which are ‘tall (or high)’ and ‘loud (or loudly)’. On the other hand, when you use it in the feminine and proceed it with the verb ‘receber‘ (to receive), it means to be discharged or released, as in from a hospital. Technically, the phrase should be ‘receber alta hospitalar‘, where hospitalar means ‘that which pertains to a hospital’, but no one uses it in my experience. As for why ‘alta’ is used and not something more seemingly sensible, at least from a native English-speaker’s standpoint, like ‘descarga‘ (discharge), I haven’t the slightest (though ‘receber descarga‘ might be understood as a ‘…descarga elétrica‘, or electric shock).
Ex. Ele recebeu alta do hospital ontem.
Ex. He was released from the hospital yesterday.