Definition - What does Email Thread mean?
An email thread is an email message that includes a running list of all the succeeding replies starting with the original email. The replies are arranged visually near the original message, usually in chronological order from the first reply to the most recent. This order is useful for the readers following the conversation because it is arranged in some hierarchical structure and may be arranged from top to bottom or vice versa depending on the email client or email provider used. Usually, the topmost email is the latest one.
Techopedia explains Email Thread
An email thread contains all the emails sent between correspondents and is very useful for documentation purposes, allowing peers to keep track of past conversations. However, email threading can be an annoyance when the topic drifts off or when the conversation becomes quite lengthy. Large numbers of replies can become overwhelming considering that users of the flat or linear style, the most commonly used structure, may attach their replies to the most recent post by default, regardless of which post they are actually replying to. This is a significant downside of the linear display mode on any email thread; it can confuse everyone involved in the discussion.
Because of the wide use of email, the use of email threading tools is being promoted by organizations in order to make communication more efficient. Using these tools can greatly increase efficiency by organizing emails in such way that redundancy is limited and the readers may be able to focus on the important parts of the email discussions.