Here is a (growing) list of terms and ideas for your reference as you navigate the site. The terms will be defined (and therefore linked) as soon as they are introduced in the lessons, so as not to scare the uninitiated. They will not be discussed here as thoroughly as they are in the lesson(s) in which they are introduced, as this is simply a reference. Accordingly, the corresponding lessons are linked within the definition as well.

- Bijective Function
- Cardinality of a Set
- Cartesian Product
- Category
- Codomain
- Composition (of functions)
- Disjoint Union
- Domain
- Element
- Endomorphism
- Epimorphism (group)
- Function
- Group
- Groupoid
- Homomorphism (group)
- Homomorphism (monoid)
- Homomorphism (ring)
- Image (of a function)
- Image (of an element)
- Injective Function
- Intersection
- Isomorphism (group)
- Modular Arithmetic
- Monoid
- Morphism
- Natural Number
- Prime Numbers
- Quotient (group)
- Ring
- Set
- Subset
- Subgroup
- Surjective Function
- Topological Space
- Union

With more lessons comes more definitions!