To bulkify your code means to combine repetitive tasks in Apex! It’s the only way to get around Governor Limits – especially our #1 most important limit! Before I give you an example, it’s important to know exactly why you need to bulkify: Up to 200 records can enter your trigger at once!
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 initiateApex, a single instance of that Apex code is executed, but it needs to handle all of the records in that given batch.