Total internal reflection fluorescence is a technique where only a very thin section close to the coverslip is excited. This makes it great for studying events in the cell membrane. The technique relies on refraction between the coverslip and the aqueous sample so only really works with living samples. The LMCF TIRF system has an incubator to keep the cells happy.

duke lmcf basis of TIRF microscopy
This diagram from the Leica brochure nicely explains TIRF. The excitation from a laser is sent off-center up a high-NA objective. The light hits the coverslip at an angle such that total internal reflection occurs and light passes through the coverslip and generates an evanescent wave. This layer of excitation might be only 100 nm thick, much less than the z-axis resolution of a confocal.

Aside from the special mode of excitation, the rest of the imaging is the same as a normal fluorescence microscope.
duke lmcf comparison of widefield fluorescence and tirf images
Here are some examples of differences between imaging in widefield and TIRF.