The load average is calculated as the average number of runnable or running tasks (R state), and the number of tasks in uninterruptible sleep (D state) over the specified interval. You can read the man pages of Linux to get more details.
It s a value calculated by measuring the OS and doing some math.. It basically tries to tell you how loaded your system is.
They are tasks.. They are closely related with the processes but they are not the same. They are basically, a set of instructions loaded into the memory. Cpu executes them.. So they are closely related but they are more fundemental.. So, generally speaking, there is a strong and positive corelation between task and process count. However; there are cases where you see one heavy process runs parallel threads, each doing some tasks concurrently and that increases the load average dramatically.. So I guess you understand the concept.