The following is the Merriam-Webster definition for Alma Mater.
Main Entry: al·ma ma·ter
Pronunciation: \ˌal-mə-ˈmä-tər\
Function: noun
Etymology: Latin, fostering mother
Date: 1651
1 : a school, college, or university which one has attended or from which one has graduated
2 : the song or hymn of a school, college, or university
This could have some connection with Chuck's past at Stanford. However, fostering mother could relate to Ellie in some way. I guess we'll find out tonight at 8:00 PM on NBC.