1. threads and processes
Popular explanations:
For the operating system, a task is a process (Process), such as opening a browser is to start a browser process, open a notepad started the process a notepad, open two notepad started the two notes this process, open a Word started the process a Word. Some processes are also doing more than one thing at the same time, such as Word, it can be carried out simultaneously typing, spell checking, printing and other things. Within a process, and more things to be doing at the same time, you need to run multiple "sub-tasks", we put these "sub-tasks" in the process is called a thread (Thread).