[English Bowman]

An endless string is the type that you are most likely to see on a recurve. It is made by looping the string material around posts several times then serving (whipping) the ends to make the loops for the nocks.
A laid in string has the loop(s) made by laying in or platting the end loops. These have no serving on the end loops and are most often seen on longbows. If that isn't clear let me know and I'll post a couple of pics

Daniel