What is the smallest 3x3 magic square?

Could you please elaborate on what a 3x3 magic square is, and then guide me towards understanding what the smallest 3x3 magic square might be? I'm curious to know if there's a specific criteria for determining the 'smallest' in this context, or if it simply refers to the numerical values within the square. Additionally, I'm interested in learning about the properties and significance of a 3x3 magic square in general.