The acronym TSP stands for 'Tax-Sheltered Annuity Plan' and TBS stands for 'Tax-Deferred Savings Plan'. Both are retirement savings plans that allow individuals to save money on a pre-tax basis. The money saved in these plans is not taxed until it is withdrawn, allowing individuals to save more money for retirement. The AMT (3 letters) stands for 'Alternative Minimum Tax', which is a tax imposed on individuals who have high incomes and/or large amounts of investments.