This relationship, then, is mandatory-optional. There may also be optional-optional relationships. For example, the relationship 'Banks Finance Cars' is optional-optional, because you can have a bank that doesn't finance cars, and there are cars that are not financed. This is an awkward and unfortunate use of the term because the optionality of a relationship could be either optional or mandatory. While an optional optionality appears redundant, it is not as bad as the seeming contradiction of a mandatory optionality.
Modality is a term from modal logic.
Modality is, in fact, a more accurate, meaningful, and less-confusing term than optionality, and is the one that I use in this series of articles. By now you have probably noticed that the bar specifying a cardinality of one can usually be inferred, because a cardinality of zero is impossible. However, the cardinality bar does serve a purpose. Because modelers do not always know the cardinality of a relationship, they must have a way to distinguish not knowing from one. Note that many tool vendors do not require, nor do some allow, a bar for a cardinality of one.