Parallelization in terms of Talend Jobs means to accomplish technical processes through parallel executions. When properly designed, a parallelization-enabled technical process can be completed within a shorter time frame.
Parallelization is an advanced feature and requires basic knowledge about a Talend Job such as how to design and execute a Job or a subJob, how to use components and how to use the different types of connections that link components or Jobs. If you feel that you need to acquire this kind of knowledge, see What is a Job design?.
Talend Studio allows you to implement different types of parallelization depending on ranging circumstances.