Citation databases include a record of citations between publications. These databases are developed for evaluating publications e.g. to see citation counts and the most cited publications/authors in a certain database.
Citation databases cover mostly journal articles but also may cover books, conference papers, dissertations, reports. No citation database covers all publications. Certain disciplines (e.g. the sciences) have better coverage in databases than others (e.g. the arts).
Citation analysis represents the attention the scientific articles receive i.e. how often a publication is cited in other publications.
Citation analysis is not a qulity indicator. Highly cited publications are often considered being of high scientific quality but the number of citations may also indicate a controversial theme.
Citation analysis finds only the citations to the publications included in the citation database. If a publication is not included in any citation database, its attention through citations stays out of reach.
Research impact indicators are not comparable across disciplines, because of differences in the most typical publishing patterns, the accumulation speed of citations and co-authoring prevalence. Discipline-based citing practices are universal.