A balance sheet lists the assets, liabilities and capital structure of a company as of specific date, usually the last day of the financial period. It helps understand what the company owns, what it owes and the amount of money invested by shareholders and debt holders.  

Cash & short term investments is the sum of cash available with the company and amount invested by the company in short term investment options. Short term investment options include investment made in liquid securities which usually have maturity of less than 1 year and can be easily converted into cash. Excess cash amount, which is not required for daily business operations, is usually invested in liquid securities.  

In case of banks, this also includes cash that has been lent to other banks on a short term basis.

Cash & short term investments is on the assets side of the balance sheet in the current assets section.