ACT is a specific way of simulating the aerospike read write workloads on the disk.
ACT measures performance on basis of both Latency and throughput. The throughput is configured as part of the config file. From the Readme:
You can simulate:
1x - normal load (2000 reads/sec and 1000 writes/sec per drive)
3x - high load (6000 reads/sec and 3000 writes/sec per drive)
any other stress load or high-performance load (custom configurable)