Attention Line: In big firms, when the writer expects that a particular person of the firm! institute should receive the letter, he only should pay attention and do the needful then the name of that person is mentioned as part of attention line. For example.
Shri Himanshu Patel
The Orient Tracking Company
Gandhi Road, Ahmedabad - 380 001
For the attention of Shri Suresh Mehta OR
Attention: Shri Suresh Mehta
Generally it is placed between inside address and salutation. It is done to draw the attention of the desired person.