The negative sign will have an effect in terms of which way the graph opens up. Since the function starts off negatively the graph will open down, like an upside down U. Rather if the function started off positive I.e Y=x^2 the graph will open upwards like a upright U.
If you have an algebraic expression in front of you and see a number there, you could label it as "known" or "a known quantity." Another word that comes to mind is "constant."
