Impasto painting uses thick, wet strokes of paint, generally applied loosely. It's frequently used in oil painting, with paint strokes so thick they may even cast their own shadows. Highlights in particular get really thick, and increase the illusion of sparkle because, not only is the paint a highlight, but the physical paint gets an actual highlight on it because of its thickness. Impressionists used Impasto heavily, such as Van Gogh and Monet. Here is a detail of Rembrandt's A Jewish Bride, showing the impasto technique clearly.
Other artists who use impasto: