Definition of estimation:
An estimation is used to assign a measurable value to the work that must be done to complete a project or task. An estimate seeks to determine the effort or cost of a project or task.
It is important that when estimating stories, the team has a shared awareness of the "value" of the estimate. Regardless of whether a team uses the [Fibonacci sequence](/en/agile-dictionary/fibonacci sequence/ "Fibonacci Numbers in Scrum") sequence, t-shirt sizes, or other values.