Set is collection of distinct objects. Notation: A = {1, 2, 3} or {x | x < 5, x ∈ ℕ}. Elements: x ∈ A (x belongs to A), x ∉ A (x not in A). Cardinality |A| = number of elements. Empty set ∅ or {} has |∅| = 0. Universal set U contains all elements under consideration. Representation: (1) Roster form: list all elements {1, 2, 3, 4, 5}; (2) Set-builder form: {x | P(x)} where P(x) is property. Example: A = {x | x is prime, x < 10} = {2, 3, 5, 7}. Solving: Identify whether set is finite/infinite, elements clearly. Exam tip: Use set notation correctly. Distinguish between {3} and 3. Understand ∈ and ⊂ carefully.