Terms needed to understand asset allocation:
Domestic Stocks = US Companies
Market Capitalization of US Stocks (According to Morningstar):
Large Cap = US Companies with a Market Cap greater than $11 Billion (these are the companies that are household names like Wal-Mart, GE, Home Depot, Coca-Cola, Pfizer, and so forth)
Mid Cap = US Companies with a Market Cap between $2-$11 Billion (these are companies that you might have heard of like HR Block, but are not the size of the previous listed group.
Small Cap = US Companies with a Market Cap below $2 Billion. Probably not going to recognize the small company unless you specifically use their product or they are in your town.
For more terms, visit the show notes at http://www.moneyguy.com/2007/10/asset-allocation-basics