Definition #1 (Beginning of time to August 2004): a survey of the public or of a sample of public opinion to acquire information. If done properly, results supposedly accurate to plus or minus 3%.
Definition #2 (September 2004 to ________): a completely illogical collection of numbers that might reflect some opinions but cannot be trusted to represent the population as a whole since polling data is obviously just a predictor and has little if any factual content.
When it was Kerry 47% and Bush 46% these polls were apparently healthy.
Now that it is Bush 55% and Kerry 42% these polls have more holes that swiss cheese.