Term: Parts of the expression separated by addition and subtraction.
For example, in the expression above, the three terms are $2x$, $3\left(5-2x\right)$, and $8$.
The expression $5-2x$ has two terms, $5$ and $2x$.

Coefficient: The number that a variable is multiplied by. In the example above, $2$ is the coefficient of $2x$.
In the expression $7x-15x^2$, both $7$ and $15$ are coefficients.

Constant: A number that is not multiplied by a variable. In the example, $8$ is a constant.
 $3$ is not a constant because it is multiplied by a variable inside the parentheses. 

Factor: Part of a multiplication expression. In the example, $2$ and $x$ are factors.
So are $3$ and $5-2x$.