Since you are only focusing on ‘3x’ and ‘2’ I’ll go from general idea to more specific. Both 3x and 2 are terms. 2 is a constant. 3x is a coefficient (3) and a variable (x).
Constant: A constant in math is a value that doesn't change.
Term: In Algebra a term is either a single number or variable, or numbers and variables multiplied together.
Coefficient: In math a coefficient is the integer beside the variable
Variable: an unknown quantity we replace with a letter
I worked very hard on this explanation so I really hope this helps!