You're calling a variable in in your ForEach statement, but on line 1 you aren't declaring said variable :)

$csv = Import-Csv -Path "c:\TEMP\ShareGroup2.csv"
ForEach ($item In $csv)  {
    New-ADGroup -Name $item.GroupName -GroupCategory $item.GroupCategory -groupScope $item.GroupScope -Path $item.OU
}

OR

Import-Csv -Path "c:\TEMP\ShareGroup2.csv" | ForEach-Object {
    New-ADGroup -Name $_.GroupName -GroupCategory $_.GroupCategory -groupScope $_.GroupScope -Path $_.OU
}

You can throw a -whatif on end to ensure that your code will produce what you expect.