"Low Latency" refers to one of the possible sides of high performance, in particular minimizing the time it takes a system to produce an output from the instant where an event is detected.
While there is a common ground to all optimizations (make the most out of the hardware) the type of work and optimizations to perform is quite different than when optimizing for high throughput or for high loads, and in many cases they are contradictory goals: optimizing for latency will in many cases reduce the overall performance of a system in ensuring that the response is fast.
This type of goals is quite common in financial systems, where being the first is the difference between getting the best price in a trade, or not even being able to execute the order at all.
As of the technologies that are related to this context, they usually range from good knowledge of the platform (hardware and OS) where the code will run, knowledge of performance measuring and tuning, multithreading and usually knowledge of networks.