What is a thread?

A thread is most fundamental unit of a computer program which is under execution independent of other parts.A thread and a task are similar and often confused.An operating system executes a program by allocating it certain resources like memory,CPU cycles and when there are many a programs doing several things corresponding to several users requests.In such a scenario each program is viewed as a 'task' by OS for which it identifies an allocate resources. An OS treats each application e.g. Word Processor,spreadsheet,email client etc as a separate task , if a certain program initiates some parallel activity e.g. doing some IO operations,printing then a 'thread' will be created fro doing this job.