A "gift" is any transfer of an asset for less than full consideration (usually no consideration). The annual exclusion (both per donor and per donee) is currently $14,000 per calendar year. There is no limit to the number of donee's that you can gift.
While the gift is not taxable to the recipient, it is also not deductible (other than charitable gifts) by the donor. The recipient will take the "tax basis" of the donor for income tax purposes.
If the $14,000 per year done rule is exceeded during the calendar year, a gift tax return (Form 709) should be filed by April 15th of the following year. No actual gift tax will be paid to the I.R.S. until the taxable portion of the gift(s) exceeds $1,000,000 per donor.
Needless to say, this is a complex area and I recommend consulting a tax professional if contemplating gifts that exceed the $14,000 per year limit.