When you plod, you walk slowly, heavily, and deliberately. You might need to plod through the snow to get to the bus stop on time.
Plod evokes a difficulty in walking — like when you trudge through mud or walk slowly up a steep hill. You might plod home at the end of a long day, or plod through an overgrown field on a hot afternoon. You can also use plod figuratively to mean "work on something boring or monotonous." The origin of plod is unknown, but it may have come from the sound of feet on the ground — the sound you make when you plod.