ALE -- Address Latch Enable.
8051 multiplexes data and address bus in AD0-AD7 pins.
the same pins AD0-AD7 carries address A0-A7 when address is sent.
carries data D0-D7 when it carries data.
to indicate when it carries address, ALE is emitted by 8051.
so use ALE as latch signal with AD0-AD7 , and you get the output as A0-A7.