Difference between -pthread and -pthreads for C/C++ on Ubuntu 14.04

I'm currently trying to compile the http://ift.tt/wMMzt2 on Ubuntu 14.04 LTS but it is failing. On CMake logs, I see errors regarding the "-pthreads" library not being found, but it finds the "-pthread" without problem. What is the difference between both? Is there any specific package for the -pthreads on Ubuntu?