What is a secure boot (on the windows 11)

Sometimes a random window flashes by on my new laptop and today it stayed open long enough for me to see it said "Secure boot" on the tab and I dont know what this is or why it opens itself randomly and then closes down again. It says on google that its a thing which comes on with you start your laptop to protect it but it flashes by for me when my laptop has been on for hours already.