It means that your potential customer requires 3 quotes before making a decision about outsourcing any work. (As Neil above stated)
If you are quoting, and you have not actually met and talked to this customer, do not spend any time on it at all. Just knock up your normal quote paperwork with a relevant opening paragraph and move on. In reality companies often know exactly who they are going to use and your quote is just fulfilling their business criteria.
In my experience, buying leads often leads to this sort of situation. If you are not geared up to spit out quality, great looking quotes in an almost mechanical manner, don't bother. I know many people will say that is wrong but I am only talking about my own experiences here. 3 quote companies are a pain to deal with. The chances are you will not be the cheapest, not be the best and you will not have an inside track.
The best companies are where the sale is agreed and shaken on following a meeting that has gone well, and the quote is just a minimal formal document they need to sign the contract. Then, if they need to get other quotes, I often provide them with the names of local companies I know are either massively expensive or just not very good at quoting. Either way, you have the inside track.
If you are just quoting out of the blue in response to a bought lead or a cold contact, it is your job to get the inside track, not spend time on a quote that might not even be read properly.