Monochromatic photography means exactly what it sounds like. Just one color. By picking different shades of the same color, you can highlight different areas of your photographs. Monochromatic photography is a great technique to isolate individual colors and make them really stand out!
Here is an example of a Monochromatic photograph:
photo by bgottsab
Here is another example of a Monochromatic photograph:
This photograph uses only oranges and reds to create a monochromatic photograph!
Obviously this technique is really useful and can make your photos really pop when done well.