The expression "3x" represents the product of 3 and a variable $x$. It means that whatever value $x$ takes, you multiply it by 3.

Would you like to see more details about how this expression works, or do you have any specific questions?

Here are five related questions you might find interesting:

1. What happens if $x = 5$? What is the value of $3x$?
2. How would you graph the equation $y = 3x$ on a coordinate plane?
3. What is the result if you add 5 to $3x$?
4. How does $3x$ compare to $2x$ if $x = 4$?
5. What would be the solution for $3x = 12$?

Tip: Remember, the expression $3x$ is linear, meaning that if you plot it on a graph, it forms a straight line.