Marine transgression and regression are the rising and falling of sea level over the continents. Sea level rises over the land - marine transgression, sea level retreats - marine regression.
The evidence for the marine transgressions and regressions can be found from the sedimentary rock record because these events leave characteristic rock layers - sedimentary facies. The Grand Canyon is an example that has an incomplete record of the four marine transgressions and regression of the Paleozoic