Ambiguous : A grammar is said to be ambiguous if there exists a string which can have more than one parse tree.
Example :
$A \rightarrow A / \epsilon$
The derivation for empty string can have parse trees of any length.
Inherently Ambiguous : A Language is said to be inherently ambiguous if all the grammars for that language are ambiguous.
Example :
$\left \{ a^{i}b^{j}c^{k} \,|\,i=j\,or \,j=k \right \}$
