After introducing basicity in the last video and generalizing it as closely related to nucleophilicity, Sal studies electron donors and the stability of both products and reactants. He compares and defines the two terms.

Nucleophilicity vs. Basicity. The difference between what it means to be a nucleophile and a base. [12:48]

This video explains the Bronsted-Lowry and Lewis definitions of acids and bases. [7:48]