Those files are the Time Machine local snapshots.
They are kept on the local machine so that you can restore older files when you are traveling/away from your Time Machine backup.
If you do not need those snapshots, rather than deleting them, you can turn this feature off (which will delete all the existing local backups). If you do not turn it off, Time Machine will just start creating new ones again.
My personal recommendation is to disable this "feature" (unless you have some particular need for local snapshots), especially those that have a hard drive rather than a SSD as it will create these local snapshots all the way up until your drive is 80% full which can (read "will" - imho) slow down the entire operation of your computer.
To disable:
Open "Terminal" - which is located in Applications / Utilites
Copy and paste the following:
then press 'return' (enter)
On the next line you will need to type in your admin password
You will not see it typed in - but it is being typed in - then press 'return' again.
You can then quit Terminal.
To verify whether these snapshots are turned on or off:
Open Time Machine Preferences - If you see:
"Time Machine keeps:" - local snapshots are off
"Time Machine keeps local snapshots as space permits and:" - local snapshots are on
This "feature", which began with OS X 10.7 is enabled by default on all Mac notebooks - it is not enabled by default on Mac desktops.