Transcluding content is simply a method of reproducing material across MEpedia, so that when it is updated in one place, it will be automatically updated in all the places where it appears. This is usually accomplished by embedding template pages into regular pages. When the template page is updated, all the regular pages that have embedded it will be updated automatically.
But transclusion is not just for template pages. For instance, a "Category:" page of researchers from a given country might be embedded ("transcluded") into the regular page about that country. In this case, the country page will display a full list of that country's researchers. If a new researcher is later added to the "Category:" page, the country page will automatically be updated as well.