What do you understand by functional dependency and transitive dependency in DBMS?

Functional Dependency
 
A functional dependency is a constraint that is used in describing the relationship among different attributes in a relation.
 
Example:
 
Consider a relation “A1” having attributes X and Y. The functional dependency among these two attributes will be:
x->Y
 
Transitive Dependency
 
A transitive dependency is a constraint which can only occur in a relation of three or more attributes. 
 
Example:
 
Consider a relation “A1” having attributes X, Y, and Z. Now, X->Z is said to hold transitive dependency, only if the following functional dependencies holds true:
X->Y
Y doesn’t -> X
Y -> Z