What is the difference between single threaded and multithreaded in java?

A single threaded application is one that has only one thread of execution running at any given point of time. Whereas a multi-threaded application can have multiple threads of executing running simultaneously.

Generally in enterprise applications, we need to fetch and load a lot of data before the system starts or initializes. In such cases, we typically spawn multiple threads and let the load operations run in parallel to save time. Lets say you need to fetch 10 different sets of data each of which will run for approximately 1 minute, if you run them all in sequence one by one, your system will load only after 10 minutes. But, if you spawn 10 threads, the system might load in around 2 minutes which is much faster than the single threaded time.