Field
Vector space
Ring
Algebra
Group
Linear transformation of vector spaces (more on this below)
Homomorphism of rings
Homomorphism of algebras
Homomorphism of groups
Independence and span
Basis and dimension
Subspace
Sum and intersection
Direct sum; interpretation in terms of idempotents
Coordinatization
Change of basis
Quotient space
Matrix representation, similarity
Kernel and image
Rank/nullity theorem
Induced map on dual spaces
Quotient maps
Canonical pairing
Dual basis
Double dual
Annihilators
Polynomials (definition, degree,...)
Ideals
Lagrange interpolation
Division algorithm
Roots and linear factors
Every ideal is principal in certain rings
Greatest common divisors
Unique factorization
Factorization over algebraically closed fields
Quotient rings
Root adjunction
Multilinear alternating functions
Existence and uniqueness of determinants
Cofactor expansions
Explicit formula with one term for each permutation
Criterion for invertibility
Cramer's rule
Vector space with basis
Direct sum
Quotient
Polynomial algebra