A third party cell phone charger is any product that is not officially endorsed and made by the manufacturer of your cell phone.  Every cell phone comes with its own charger, in some cases the same charger can be used on multiple phone models but in others it is exclusive to a given cell phone.  Any other charger you use that is made by someone else is considered a third party cell phone charger.  While most third party chargers will work with a cell phone, they are not guaranteed to work by the maker or your cell phone maker.  You may find one brand works for your phone whereas another does not.

Most affiliate cell phone stores carry third party chargers where most branded stores, like a Verizon Wireless location or AT&T location would not. The cell phone companies want you to spend the most they can get out of you by forcing you into buying an approved cell phone charger. They will steer you away from third party chargers, because they are cheaper and they do not make as much money from them.

However, finding a third party cell phone charger on your own is rather easy. You want to know the make and model of your phone, then check the packaging of a set of chargers. Most stores that carry third party chargers have them grouped by cell phone maker which makes it easier for you to narrow down which one will work. The package will list which phone the charger is compatible with so you can find yours and you are good to go. Third party cell phone chargers come in car and home chargers, so you will be able to find one that works with your phone.

Some argue third party cell phone chargers are bad for cell phones.  In some cases, cell phone makers go out of their way to ensure third party products do not work with their phones.  If this is the case with your phone, a third party cell phone charger will simply not work, it will not damage your phone no matter what a sales associate might tell you.