A lemon is a slang term for a motor vehicle that is so packed with faults from manufacture that it's unfixable and useless. In popular mythology, these vehicles are manufactured on Friday afternoon. In the USA, so-called Lemon Laws or Lemon Statutes in most States offer the consumer some protection against new cars that break down so often in the first year or so that they might as well be on the road to nowhere. Most of these statutes allow the consumer to get a replacement or a refund if the official lemon definition, which varies from state to state, is met, but typically:

"Generally, if the car has been repaired 4 or more times for the same Defect within the Warranty Period and the Defect has not been fixed, the car qualifies as a Lemon." (http://www.carlemon.com/, 2001-11-01)

California also has a so-called "Puppy Lemon Law", the Lockyer-Polanco-Farr Pet Protection Act, Section 122125 of the California Health and Safety Code. This gives you consumer rights if the new dog or cat you purchase turns out to be a crippled, disease-riddled, psychotic fleabag. In particular, for up to a year after the date of purchase, if a veterinarian finds a congenital or hereditary condition in the dog or cat, you can get a refund, replacement, or vet's bills paid. (Sigh, if only this applied to children also.)