The holding period is the length of time you held an asset. It's generally measured from the day you purchase the asset through the day you sell it.
Holding periods can be either long-term or short-term. A long-term holding period is one in which you hold an asset for more than 1 year. If you hold an asset for a year or less, it's considered a short-term holding period. The holding period is important because it determines whether the gain on your sale will be taxed at a favorable rate (long-term) or at the same rate as the rest of your income (short-term).
The holding period of assets received as a gift may include the donor's holding period. The holding period of inherited assets is always long-term.