Since issues often represent a single unit of work that can be worked on, it is logical for users to log the time they have spent working on it. You can specify an estimated effort required to complete an issue, and JIRA will be able to help you track the progress. JIRA displays the time tracking information of an issue in the Time Tracking panel at the right-hand side, as shown in the following screenshot with its description:
Estimated: This represents the original estimated effort required to complete the issue. For example, the estimated time required for fixing a bug by a developer.
Remaining: This represents the remaining time for the issue to be completed. It is calculated automatically by JIRA based on the original estimate and total time logged by users. However, the user logging work on the issue, as described in the following section, can also override this value.
Logged: This represents the total time spent on the issue so far.