Can someone explain what is *lock pages in memory*

yes, suppose Court (judiciary system) has put someone in prison, but then the jailor let him free. It will create chaos, isn't it? the jailor should not be allowed to let anyone free until granted by the court.

 judiciary system = SQL Server 

 Prison= RAM (Memory)

so, if SQL Server puts some data in RAM then it should remain in the RAM, this is how SQL Server gives you performance, and Windows OS (jailor) shouldn't allow to pull data out from the RAM, so it is better to lock pages (The disk space allocated to a data file (.mdf or .ndf) in a database is logically divided into pages numbered contiguously from 0 to n. Disk I/O operations are performed at the page level.).

To enable the lock pages in the memory option

• On the Start menu, click Run. In the Open box, type gpedit.msc.
• On the Local Group Policy Editor console, expand Computer Configuration, and then expand Windows Settings.
• Expand Security Settings, and then expand Local Policies.
• Select the User Rights Assignment folder.
• The policies will be displayed in the details pane.
• In the pane, double-click Lock pages in memory.
• In the Local Security Setting - Lock pages in the memory dialog box, click Add User or Group.
• In the Select Users, Service Accounts, or Groups dialog box, select the SQL Server Service account.
• Restart the SQL Server Service for this setting to take effect.