A V-visa is a temporary visa obtainable by spouses and minor, unmarried children under the age of 21of holders of U.S. Green Cards. The V-Visa allows these families to unite during the immigration process. The visa was made possible by the Legal Immigration Family Equity Act of 2000. This law was passed in order to relieve those who applied for immigrant visas on or before December 21, 2000. From a practical standpoint, the V visa is currently unavailable to spouses and minor children for who petitions were filed after this date.
A Green Card holder who marries a foreigner/alien or another permanent resident should file a petition with the USCIS. Once that petition is approved, the spouse must wait for an F2A immigrant visa to become available. Unfortunately, the F2A immigrant visa is subject to long backlogging since approximately 90,000 visas are available each year and more people want them than that which are available.
You can check the U.S.C.I.S. website to gauge the processing times. During the backlog however, the beneficiary may temporarily visit the U.S. on B-2 visa (maximum 90 or 180 days stay) or under the Visa Waiver Program (VWP, maximum 90 days stay). Keep in mind though that in a lot of cases, application for these will be denied since immigration will not be convinced that your stay will really be temporary since your spouse lives here.
You will therefore have a difficult time proving “nonimmigrant intent.” This can lead to a two-year wait for such families to be united.