The expression given is $3x + 1$. This expression is a polynomial with two terms: $3x$ and $1$.

Since it consists of two terms, it is specifically called a binomial.

Would you like more details or have any questions?

Here are five related questions:

1. What is a monomial, and how does it differ from a binomial?
2. Can a polynomial have more than two terms? What is it called if it does?
3. How can you determine the degree of a polynomial?
4. What are the coefficients in the polynomial $3x + 1$?
5. How would you add or subtract two binomials?

Tip: The degree of a polynomial is determined by the highest power of the variable within it.