spinning a prop

[syd]

I have heard this term before. I have heard boat owners say they have spun a prop. I am a relatively new boat owner omly 2 or 3 years still learning. What is spinning a prop, can you do something to prevent it. Plus as far as boat maintenance goes i have my lower unit fluid changed each year around thanksgiving, change spark plugs at least once a year and use stabil each time i gas up to prevent ethanol issues and winterize.
Is there anything else i need to be doing preventive maintenance wise.

thank you