May/December relationships can either be superficial or serious - so the term doesn't itself say anything about the status of the relationship.
Basically any kind of involved relationship where there is a substantial age difference between the two people and the relationship does not consist of either partner being considered legally underage (which is commonly known as pedophilia which is something else entirely).
2. Lynda is 48 yrs old but she's a total cougar cus she's dating a 22 yr old boy named Devon; they have a May December relationship.
3. Mr.Smith is 50 and Mrs.Smith is 26. They have been married for 2 years and are in a May/December relationship.