Serial Vs Sequence

Dear all,

I am not able to distinct these two datatypes ( Serial and Sequence ) in
Postgresql which resembles like auto-increment in Mysql.

Which one gets priority and When ?

The only thing I am able to find is to use SERIAL because if a drop
table occurs , still SEQUENCE memory is not freed, its garbage remains.

However if we define a SERIAL column in a table , implicitly it makes a
sequence.

Could anyone Please describe me the difference and Which to Use When ?


Thanks & Regards

Adarsh Sharma