Once you have some search results, you will need to decide which articles you will actually use in your literature review. This can be done using filters/limits in the databases, applying inclusion/exclusion criteria, and appraising the articles.
Filters and limits (the name varies by database) are tools the database provides to help you narrow your search results. Different databases offer different filters, but these are some of the more common ones you'll find.
Your search terms and the filters/limits you apply are generally not enough to narrow your results to the most relevant and highest quality studies for your project. The final step to selecting these studies is to apply your inclusion and exclusion criteria. Basically, these are the reasons why you keep (include) or reject (exclude) articles as you look through the results, reading titles and abstracts (and sometimes the whole article)
Examples of types of Inclusion/Exclusion Criteria
Filters and Limits
Inclusion and Exclusion Criteria