Sounds like woolly aphids from here.

Dan

I'll guess that they're mealybugs. A picture would be helpful.

Potted lemons are also prey to scale. A trick told me by a citrus specialist to get rid of scale and which I think would also work for wolly aphid or mealy bugs is to go over every twig and leaf with babywipes. It takes a while but is quite a relaxing job and definitely works. My Myer lemon gets scale most winters when it comes indoors but it is easily fixed. Lemons don't want to be too warm in winter just as long as they stay above freezing.

I can go with scale too. Until we have pix, all guesswork tho. When I used to live in CA I'd control scale and the other critters mentioned above with a soapy oil spray in a quart bottle and a strip of tanglefoot on tape affixed to the trunk to stop the crawlers.

Dan