ACID stands for Atomicity, Consistency, Isolation, and Durability.
Until Hive 0.13, ACID properties were provided only at the partition level. For Isolation, you would have to turn on one of the available locking mechanisms (ZooKeeper or in memory). But in Hive 0.13(and above) due to the addition of transactions, it is possible to provide full ACID semantics at the low level, so that one application can add rows while another reads from the same partition without interfering with each other.