Without a definition. If speaking in terms of God, undefined can refer to having no set standards. The amount of love God has for us is undefined, such as there is not a word that can describe such a large amount.
In math (hence it being under homework help) undefined means on a graph, when you have a line that is graphed and it is going straight up and down. the equation of a line is y=mx+b y being your y coordinate m being your slope (rise/run) x being your x coordinate and b is your y-intercept (where the line will cross the y axis) so if you had this y=2x+1 you could plug in any x value (which it's easier to work with smaller numbers so you start plugging in smaller numbers) and when you plug in your x value, solve for y. when you solved for y you should have a point you can graph for your line at (x,y) x being the x value you plugged into the equation and y being the number you got as your answer out of it.
basically to sum it up, an undefined line is referring to the slope. since graphs are read from left to right, if the line is going up to the right, it is a positive m or slope. if it is going down and to the right the m or slope is negative. if the line goes straight across without going up or down, the slope (m) is zero. it is only when it goes up and down when it is undefined.