It depends...
If you are a mortgage lender, it's all of your cash, stocks, bonds, even IRAs and 401k's.
This is a ridiculous way of calculating as anyone who treats an IRA as liquid is asking for trouble. A mortgage lender does it to factor it into whether or not you could pony up for mortgage payments if you lost your job for a while.
Any sort of financial advisor will tell you that your liquid assets are anything you can convert to cash in 30 days without losing money. Withdrawal penalties and fees take IRAs, 401Ks and by many people's measure's stocks too. By this definition, you add up your checking and savings accounts, CDs, and any other cashlike instruments...