The time entry is an activity. What distinguishes an activity from a time entry are the configurations and use of each.
Activity
An activity represents a task performed or to be performed on a given date.
When you add an activity and it is a fee activity, you have the option to enter a time entry:
This time entry will be used to calculate the value of the activity. For example, a time entry of 2 hours at a rate of $150/hr will result in an activity value of $300.
Ultimately, it is the activities that are part of the bill.
Time entry
When you enter time through the timesheet, it creates a fee activity.
To view it, just double-click on the time entry:
This gives you access to the activity.
*Note that since the activity was created via the timesheet, the time entry is automatically entered there.