Coaxial Cable in general is a two conductor flexible cable for RF or audio transmission (depending upon the application and type). There is usually a center copper/brass or aluminum conductor wrapped with a dielectric polyfoam insullator. That is then covered with a brass/copper or aluminum braid that "shields" the center conductor from any outside influences such as random noise or another radio system close by. The braid is then covered with an outside protective layer which is weather resistant and in some cases UV resistant. The term Co-axial refers to the (normally) two conductors separated by an insullator and configured in the same plane or axis (axial).
There are various types for many different applications and based upon needs and budget, there are many that would work for you. Give us some idea of the distance that will be between the radio and antenna, the type of antenna that you may wish to use and the frequencies that you will be listening to, so we can make some suggestions that are within your budget.
