These are referred to informally as subclasses in the community. Although the term does not appear in the core books or System Reference Document, the designers of 5e have used this term in Sage Advice rulings, and the following appears in the introductory passages to the expansion book Xanathar's Guide to Everything (emphasis mine):
Each class offers a character-defining choice at 1st, 2nd, or 3rd level that unlocks a series of special features, not available to the class as a whole. That choice is called a subclass.
Another commonly used term in the community is archetype, which is actually used in the names of the Roguish Archetype, Ranger Archetype (tentatively revised to Ranger Conclave in an Unearthed Arcana revision), and the Martial Archetype of the Fighter.
Finally, the properties that characters get from their classes are called features, and when there is a choice among several features they are often called options. Therefore, you can call the collection of game features that a character gets from their chosen subclass by any of the following phrases and you would probably be understood in any circle of people familiar with 5e: subclass features, subclass options, archetype features, or archetype options.