A target-date fund includes a collection of assets, typically stocks and bonds, that evolves over time to facilitate the investor’s capital needs at the target date.
The Vanguard target-date 2040 fund (VFORX) is intended for an investor that will start selling the fund around the year 2040. This fund holds about 85 percent stocks (15 percent bonds) at the time of this writing but will likely increase bond and decrease stock holdings in the upcoming 20 years.
Investor.gov article on target date funds
Investopedia's article on target-date funds