Inactive users are created in AD and not used for certain number of days. Its a security risk leaving the inactive users in AD.
How to find the inactive users in AD using powershell.
Search-ADAccount -AccountInactive -TimeSpan 60 -UsersOnly | Where-Object { $_.Enabled -eq $true } | Format-Table Name, UserPrincipalName, DistinguishedName
How to disable these inactive users in AD using powershell
Search-ADAccount -AccountInactive -TimeSpan 60 -UsersOnly | Where-Object { $_.Enabled -eq $true } | Disable-ADAccount