What is a courier service?

I need to send in a stock certificate. They told me to use a courier service. What exactly does that mean? Is that something the post office offers, or does it mean use someone other than the post office, like UPS?

Post Office is ok. Make it registered as the document is important.

no this is better and i dont know how to get a job doing it..say you have something pretty valuable that needs to get from point a to point b say LA to sydney. A individual such as myself will get a plane ticket and actually take this item to where and whom it needs to go..it never leaves my possession until the proper poeple get it.

ups, fed ex. you can do it at the post office too.

ya it does the same work what the post office does, but the difference is the how effective is the work.......the courier people do the same work more effectively means in much less time when u compare with post office work........the only condition is the courier service must have its service at that particular place where we desire to send that parcel.

another word for it would be messenger services
thats the same as a courier,,
plus they can deliver in hours.. UPS/Fedex takes at least
1 day