Lockstep synchronization involves two or more similar devices sharing the same timing and triggering and essentially acting as a single device. Sharing a sample clock between analog input and analog output operations on a single device is also considered lockstep synchronization. The goal of lockstep synchronization is to eliminate skew as much as possible. In lockstep synchronization, clocks and triggers are typically shared.
Handshaked synchronization (or stimulus/response) is two or more devices acting in sequence. In handshaked synchronization, triggers and events are typically shared. A simplified DAC test is an example of this type of synchronization. A digital device sends a digital pattern to the DAC and a signal causing the DAC to create a voltage in response to this pattern. At the same time or soon after, the digital device sends a signal to a DMM causing the DMM to measure the voltage output by the DAC. When the DMM has finished the measurement, it sends a signal back to the digital device causing the digital device to send the next pattern to the DAC.
In lockstep synchronization, the operations involved all use a clock or trigger for the same purpose. In handshaked synchronization, the roles of the trigger or event are typically reversed between the operations (for example a Sample Complete Event from a DMM is used as a Sample Clock by the digital device that receives it).