There are lots of difference between SharePoint online and SharePoint on premise version. In SharePoint on premise, the server will be maintained by your organization, but in case of SharePoint online, everything will be maintained by Microsoft, you just need to use. Similarly patches and updates will be taken CARE by Microsoft, but in on premise ENVIRONMENT, everything will be taken care by your IT team of the organization.

In SharePoint online, Microsoft does not allows you to deploy any server side CODE but we can develop and deploy SOLUTIONS USING server object model in on premise environment. Alternatively Microsoft has improved client side object model and we can develop and deploy SharePoint Add-ins using client object model.

There are lots of difference between SharePoint online and SharePoint on premise version. In SharePoint on premise, the server will be maintained by your organization, but in case of SharePoint online, everything will be maintained by Microsoft, you just need to use. Similarly patches and updates will be taken care by Microsoft, but in on premise environment, everything will be taken care by your IT team of the organization.

In SharePoint online, Microsoft does not allows you to deploy any server side code but we can develop and deploy solutions using server object model in on premise environment. Alternatively Microsoft has improved client side object model and we can develop and deploy SharePoint Add-ins using client object model.