A target retirement date fund takes risk based on expecting it's investors to retire in a specific year, say 2050.
It then follows a flight path, changing what it invests in leading up to that specific retirement date. When you're younger it will take more risk to try to maximise returns but it will slowly adjust into less risky investments, aiming to preserve your savings into retirement.
Therefore you never need to worry about changing your investments as you age. Simply pick when you want to retire and let BlackRock do the rest.
See the video for more information!