New one for me By Cathy-Dee

Most of the sites I saw were dedicated to High School math which may be why the term is not as recognized. Some of the sites mentioned the need to have it from primary grades upwards so perhaps schools are moving more towards incorporating it into the curriculum at lower grades now.

With grade 1 the only thing I can think of is that you would introduce very basic concepts within the context of problem solving and graphing.

These links may help you in figuring this out.

http://bhs.broo.k12.wv.us/discrete/DSCRTE.HTM
http://mathforum.org/library/problems/sets/elem_discrete.html

Hope this helps