There are many purposes of a math word wall. Mike's goal in creating his word wall is clear. He wanted to:
1. Make the word wall accessible by placing in a place where students can reach and read the words.
2. Attach meaning to each word by including a definition or example.
3. Make a word wall that is a learning tool, not just a display.
Mike updates his word wall regularly. Clearly, his challenge is to find room to keep all these words up.
The Guide to Effective Instruction in Mathematics K-6: Volume 3 - Classroom Resources and Management suggests that words can be moved and placed in a binder or big book to make room for new words.
This document suggests other considerations when creating a math word wall in your classroom.