What does it mean when a plant has yellow spots on it?

This might be the plants reaction to something in the water you're giving it, you might need to change how frequently you water it, or you might need to change the lighting you're giving it. This could also be from mites or other little critters eating away at your plant.

Plants' foliage will start to brown if there is an excess of fluoride or chlorine in the water you give it. You can sit the water out for a few days to distill it to fix the chlorine problem, but if there is too much fluoride in the water, you will have to find another water source.

If you're watering your plant too frequently, the roots could rot and this could end up being reflected in your plant's foliage, but this usually starts showing at the tips first. If you're not watering it enough, your plant can easily be brought back by some consistent proper watering. For some plants, it's best to let them dry out before watering them anyway.

Make sure to dust your plants' foliage regularly to help keep away mites and bugs, and to keep your plant looking healthy :)