Final answer:
The degree of the term -3mn in algebra is 2, which is calculated by adding the exponents of the variables m and n.
Step-by-step explanation:
The degree of a term in algebra represents the sum of the exponents of the variables in the term.
In the case of -3mn, there is one instance of the variable m and one instance of the variable n, both to the first power (since no exponent is written, it is understood to be 1).
Thus, the degree of this term is 1 + 1 = 2.