A solar light uses energy from the sun to produce light. (Solar light can also refer to natural light coming from the sun.)
There are inexpensive lights that you can place outside. During the day, they use solar energy to charge a battery, and at night, or when it's too dark to charge the battery, the battery runs a light. Besides not needing to pay for power for these lights, they have the advantages of coming on automatically when it gets dark and not requiring any wiring.
Solar power can also be used to provide energy for other appliances.