Coaxial and composite cable question.

This is probably a dumb question, but I wonder what the difference is in the construction of coaxial and composite cables? They look similar in the outside and they also feel similar. Could one substitute one for the other in order to hear DD or DTS surround sound? I have my DVD player hooked up to my receiver with a coaxial cable, btw. I googled this but could not come up with much, since most sites compared coaxial to fiber. Thanks for any help.