May/December relationship refers to a relationship between two people where one partner is in the "winter" of their life (old) and the other partner in the relationship is in the "spring" of their life (young). This can go either way such as the woman is older or the man is older. Being a nonspecific term, it encompasses the concept of slang words like cougar
(which is offensive if used on couples who are serious). This term is also tied to concepts such as "robbing the cradle
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).
1. Connor is 52 but his girlfriend Debbie is 25; therefore they are in a May/December relationship.
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.