In the Scrum Framework all activities needed for the implementation of entries from the Scrum Product Backlog are performed within Sprints (also called 'Iterations'). Sprints are always short: normally about 2-4 weeks.
Each Sprint follows a defined process as shown below:
The heart of Scrum is a Sprint, a time-box of two weeks or one month during which a potentially releasable product increment is created. A new Sprint starts immediately after the conclusion of the previous Sprint. Sprints consist of the Sprint planning, daily scrums, the development work, the Sprint review, and the Sprint retrospective.
In Sprint planning, the work to be performed in the Sprint is planned collaboratively by the Scrum Team.
The Daily Scrum Meeting is a 15-minute time-boxed event for the Scrum Team to synchronize the activities and create a plan for that day.
A Sprint Review is held at the end of the Sprint to inspect the Increment and make changes to the Product Backlog, if needed.
The Sprint Retrospective occurs after the Sprint Review and prior to the next Sprint Planning. In this meeting, the Scrum Team is to inspect itself and create a plan for improvements to be enacted during the subsequent Sprint.
The goal of initial release planning is to estimate roughly which features will be delivered by the release deadline (presuming the deadline is fixed), or to choose a rough delivery date for a given set of features (if scope is fixed). We use this information to decide whether or not the project will produce enough ROI to at least pay for itself, and therefore whether or not we should proceed.
Milestone is typically associated with reaching a certain goal, before proceeding forward or stopping altogether. Checkpoint signifies points at which the team stops and checks progress against expectations, and possibly adjust.
Milestone (big granularity) means progress checking at iterative way; it is important in overall project progress and if associated goal is not fulfilled, some important analysis and decisions are needed; it is associated with phases and iterations or other important points and it could be related to formal progress tracking. As “no team is an island unto itself”, that “software development” is not a hermetically sealed universe, and that the software development efforts of one team are usually part of a bigger coordinated undertaking / organization.
Now an answer to your question in short:
Sprint, Milestone and release are not same but at some point during project development they meet each other.
It may be possible end of particular milestone can result into partial/final release.
Sprints are chunks for for development plan, with iterative activities, it cannot be considered as a Milestone.