What is the difference between the 5' end and the 3' end of a nucleic acid strand?

The 5' end of a nucleic acid strand refers to the end with a phosphate group attached to the 5th carbon of the sugar molecule, while the 3' end refers to the end with a hydroxyl group attached to the 3rd carbon of the sugar molecule. This distinction is important for understanding the directionality of nucleic acid synthesis and function.