diagram
collection of objects and morphisms in a category
commutative diagram
collection of maps in which all map compositions starting from the same set and ending with the same set give the same result
span
in category theory, a generalization of the notion of relation between two objects of a category
exact sequence
sequence of homomorphisms such that each kernel equals the preceding image
chain complex
in homological algebra, a structure consisting of a sequence of modules and a sequence of homomorphisms between consecutive modules such that the image of each homomorphism is included in the kernel of the next