1. When talking about computer programming or software, a thread is a portion of a program that is executed in conjunction with the main program that performs another task. For example, a program may have an open thread waiting for a specific event to occur or may have a thread running a separate job, allowing for the main program to perform other tasks. A program is capable of having multiple threads open at once and will either terminate or suspend the thread when the thread's task is complete or the program is closed.
2. A thread is a message and each of its corresponding responses. For example, in a newsgroup or message board, a user may post a question relating to computers; each of the replies and discussions relating to the original message or replies are posted within a single thread. Below is an illustration to help give you a better idea.
<Original Message> user - firstname.lastname@example.org
Hello, I was wondering if anyone knows how to turn on a computer.
>>Joe - email@example.com
>>User have you tried pressing the power button?
>>>>User - firstname.lastname@example.org
>>>>Joe what is the power button?
>>>>>>Joe - email@example.com
>>>>>>The power button is usually a small power button located on the front of your computer, pressing this round button should make the computer turn on.
As can be seen by the above example thread, a user can view the complete message and make any additional feedback or comments as well. A thread can refer to any ongoing communication, including e-mail.