The meaning of ALE is address latch enable. This is a special pin of 8086/8088 processor. 8086 is one of the microprocessor which has multiplexed address/data lines i.e. same 16 lines are used for both address and data transfer operations (named AD0 to AD15). As these lines are multiplexed, at a time either address or data will be allowed to transfer through it. In general computer architecture, for any kind of operation (R/W), the address for the operation is generated first and then data transfer operation is performed. Means, at a time both of these operations are not performed. When processor transfers address on AD0-AD15, it makes ALE pin high to suggest the multiplexed lines contain address on it. When this pin becomes low, data is transferred after inserting some propagation delay between operations. That means, same lines will be used for multiple operations. Observe the timing diagram of this operation here.