It would have been better if you had actually given us the expression, but I will give you the most common possibility.
In the expression 3x+5, 3 is called the coefficient
n-3
add 3 to a number a number plus 3 the sum of a number and 3 3 more than a number a number increased by 3
2x+3 is an algebra or algebraic expression because an algebraic expression is one or more algebraic terms in a phrase. It can include variables, constants, and operating symbols, such as plus and minus signs. It's only a phrase, not the whole sentence, so it doesn't include an equal sign. so 2xy +3x is an algebraic expression but x+y=2 is NOT.
y me
addition