A systematic review is a very specific type of review, originally used in the medical sciences. If publishing a systematic review, check the guidelines as there are usually strict criteria regarding the structure, protocol, methodology, search methods, data extraction, screening and analysis and reporting.
Generally speaking, the 'systematic literature search' part of the review must have a clear protocol driven question, a comprehensive and replicable search strategy and a clearly documented search process.
Even if you are not undertaking/publishing a systematic review in the strictest sense, most literature searches, in all subject areas, would benefit from a more systematic approach.
It is likely that you will need to search across multiple databases and adapt your search strings to each database. You will need to balance search sensitivity and specificity (depending on your project scope).
See:
For help with systematic searching (developing your search terms, defining your inclusion/exclusion criteria, selecting and effectively searching appropriate databases, and managing your search results), please contact the Academic Librarian for your subject.
For examples of systematic reviews see:
Medicine/healthcare
Social Sciences and Environment
Cochrane reviews have very strict criteria: