Hi Arun,
The term bulkifying Apex code refers to the concept of making sure the code properly handles more than one record at a time. When a batch of records initiate Apex, a single instance of that Apex code is executed, but it needs to handle all of the records in that given batch. For example, a trigger could be invoked by an Force.com Web Services API call that inserted a batch of records. Or a custom Apex Web Service. So if a batch of records invokes the the same Apex code, all of those records need to be processed as a bulk, in order to write scalable code and avoid hitting governor limits.