[CentOS] What is Judy?

I am trying to build Miredo 1.1.5 
(http://www.remlab.net/miredo/devel.shtml.en)

I have followed the rpmbuild instructions from: 
http://www.owlriver.com/tips/non-root/, and have the miredo source in 
~/build/miredo-1.1.5.

I run ./configure (as the INSTALL text file tells me to do) and get the 
error:

checking for Judy.h usablity... no
checking for Judy.h presence... no
checking for Judy.h... no
configure: WARING: If you don't care about scalability, re-run configure 
with ' --without-Judy'.
configure: error: Required Judy dynamic arrays library missing.