Exact matches (highlighted in dark blue in the verbatim text) represent the number of documents where your search term appeared in the data set exactly as you specified. Linguistically speaking, we take into account surface and "stemmed" forms of the term/concept word.
So, for example, "buy" and "bought" would be considered exact matches, as would "Love my Kindle" and "Love the Kindle".
Conceptual matches (highlighted in light blue in the verbatim text) are up to the top 20 terms with an association score greater than 0.60 to your selected concept, which can be seen by scrolling down under Top related concepts (middle panel) when you have a concept selected.
When you search for a term, the verbatim results include a percentage of the discussion volume that includes both exact and conceptual matches for your specified term.