What is a Minecraft snapshot? and How to access Minecraft snapshots?

A Snapshot is a testing version of Minecraft, periodically released by Mojang Studios

Minecraft snapshot 

Experimenting with primitive iterations of games provides players with an opportunity to explore rudimentary features and mechanics.

Snapshot updates

From Beta 1.7.3 to Beta 1.8, Mojang began dropping beta updates for players to test and report bugs.

How to Use a Snapshot

1. Start the Minecraft launcher. 2. Click "Installations".

3. For snapshots: click "Snapshots". For beta and alpha versions: click "Historical".   4. Start up Minecraft.

What is included in new snapshots? 

Snapshots introduce new features based on the development team's priorities.