Let's get the right term

On many occasions, Lightning Experience is simply referred to as Lightning, although there are many items in the Salesforce platform which start with the word "Lightning", such as Lightning Login, Lightning App Builder, Lightning for Outlook, Lightning Components, Lightning Sync, and so on. Some of them are applicable in Lightning Experience only, but some others will work in both Lightning Experience and older Classic user interfaces, for example, Lightning Sync is used to sync your user contacts and events between your email server with Salesforce.

Just to make it clear, when you meet someone from the Salesforce community, and he asks if you are on lightning, most probably, he is referring to Lightning Experience. To get the term right, it is Lightning, not Lightening or Lighting.