SciELO and LILACS are databases covering literature from Latin America and the Caribbean, and in the case of SciELO, other places. It will include material that Medline, Embase and other “usual” sources miss.
I have seen both mentioned as sources searched for systematic reviews. In addition to that, of course, they will be useful if you have an interest in those parts of the world or health issues endemic there.
SciELO (“Scientific Electronic Library Online”) is a database of open access journal articles published in Latin America, the Caribbean, Spain, Portugal and South Africa. It is really, I think, an online publishing platform. It covers many subjects, but includes health sciences, social sciences and biological sciences. In addition to being available at www.scielo.org, SciELO Citation Index has been made available to subscribers to Web of Science. A quick search for the same topic via the usual interface and via Web of Science suggests that the two interfaces do not cover the same date range. In WoS you are of course using the standard WoS interface, although WoS subject categories are available via the usual interface. The default search interface at that "usual" place is in Portuguese (SciELO is based in Brazil), but there are interfaces in English and Spanish. I cannot see a search guide on the site, so will need to write one!
LILACS (“Latin-American and Caribbean System on Health Sciences Information”) covers health subjects only, and involves the WHO. It has an English interface, and is a database of journal articles, books and theses from Latin America and the Caribbean. Some of it is available in full text via links to SciELO. Topic specific queries available from the home page include Millennium Development Goals, gender and health and social determinants of health. There are also queries for specific study types. The FAQs tell you more about LILACS.