Workflow is an automated process that fired an action based on Evaluation criteria and rule criteria.
We can access a workflow across the object.
We cannot perform DML operation on workflow
We cannot query from database
Trigger is a piece of code that executes before or after a record is inserted or updated.
We can access the trigger across the object and related to that objects
We can use 20 DML operations in one trigger.
We can use 20 SOQL from database in one trigger.