Microsoft has updated the Office 365 Groups functionality to include connectors with social networks like Twitter or web applications like Dynamics CRM.
By default this feature is turned on.
If you want to disable it, you must use PowerShell
$cred = Get-Credential
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/powershell-liveid/ -Credential $cred -Authentication Basic -AllowRedirection
Set-OrganizationConfig -Identity contoso.com -ConnectorsEnabled:$false
When enabled (as it is by default), the connectors are available using Outlook Web Access (or now called Outlook On the Web) and click on the Connector tab
Then you will be able to add connectors
Once you have added connector(s), this Connectors tabs will also be used to configure (use the My Accounts option when on the Connector page) or remove the connector