This does get forgotten by heaps of 2U students to be fair but it's absolutely crucial.
The exponential a^x (doesn't have to specifically be e^x) has a horizontal asymptote at y=0, for very large NEGATIVE x. We say that the limit as x goes to negate infinity is therefore 0.
Because fact is if you raise a number to a really negative number it just goes down to 0
However, if you've never heard of what a limit is, then there's something that you weren't taught that belongs in 2U. I do suspect you're a VCE student but in here I use anything that belongs to the 2U course.
Another world is a WACE student
you can think about limits intuitively without the notation! Like, for the limit of something as x approaches infinity, you mean,
What happens as you pop in MASSIVE values of x. It's just a formal notation for saying, when x is HUGE, or x is HUGELY NEGATIVE (-infinity), or (less important for you), when x is REALLY CLOSE to some other value