A situationship is the form of unofficial relationship where as at least one of the parties doesn't want to be in a relationship with a title. In some cases both parties agrees, where as in most cases, one wants more, so there's a side of deception in many cases. It could be exclusive or not, clear or not, messy or not and definitely more than fuck buddies but obviously less than the official relationship.
He likes me and wants us to be exclusive but doesn't want to put the title of boyfriend/girlfriend in our relationship. This is a situationship.
An unofficial 'relationship' that remains unlabeled. Likely when two people have unsaid feelings for eachother, and are aware, but never officially start dating. Interactions can be casual, romantic, or sexual but doesn't have to be all.
"We liked each other but never really did anything about it. We were affectionate and went on dates but we didn't call them dates. It was more of a situationship than an actual relationship."