A thread is a basic unit of CPU utilization; it comprises a thread ID, a program counter, a register set, and a stack. It shares with other threads belonging to the same process its code section, data section, and other operating-system resources, such as open files and signals. A traditional (or heavyweight) process has a single thread of control.
Application
Many software packages that run on modern desktop PCs are multithreaded. An application typically is implemented as a separate process with several threads of control.