Bulkifying trigger: It refers to the concept of making sure the code properly handles more than one record at a time. When a batch of records initiates Apex, a single instance of that Apex code is executed, but it needs to handle all of the records in that given batch.
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!