What do you mean by Polytrophic acids and bases?

Bronsted acids which can donate more than one proton are called Polytrophic acids or polybasic acids. For example, oxalic acid and sulphuric acid have two ionizable protons per molecule of the acid, which can be donated. These are called dibasic acids. Phosphorous acid H₃PO₄ which can donate three protons is called tribasic acid. For example:

The dissociation reaction for a dibasic acid may be represented as:
H₂X (aq) < -----------------> H⁺ (aq) + HX^– (aq)
HX^– (aq) <----------> H⁺ (aq) + X^2- (aq)
The corresponding dissociation constants are:
K_a1 = [H⁺] [HX^–] / [H₂X]
K_a2 = [H⁺] [X^2-] / [HX^–]
K_a1 and K_a2 are called first and second ionization constants respectively of the acid H₂X.
Similarly a polyacidic base is a species which can accept more than one proton.
For example: CO₃ ^2- anion is diacidic because they can accept two protons and phosphate anion, PO₄ ^3- is a triacidic because it can accept three protons.