What does this mean in C?

-> is the equivalent of (*L).Next.  

In C, a variable (x) of a struct (A) is accessed by A.x

Now if you have a pointer (B) to the struct, you have to use (*B).x or B->x

As for_yan said, L is a pointer to a structure.  You would find out which structure by finding the declaration for L.  In this case, I would guess that this function is processing a linked list (or similar).  Here's an example (untested).

typedef Node
{
    Node *link;
    char item [ 50 ];
} Node;

int isLastElement ( struct Node *L )
{
    return L->next == NULL;
}

main()
{
   ...
   if ( isLastElement ( &Node ) )
        printf ( "We are at the last element\n" );
    ....
}

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farzanj just said what I was going to put in my next post.  He is correct as well.

Ok so like if I have a struct named L

->L is like *L  
meaning it returns the address of L... correct?

Next should be another field of the structure that give the address of the next estructure data, this type of definition is used to create a linked list.  *L = address of the current node of the structure
L->next = address of the next node of the structure

check the following
http://gd.tuwien.ac.at/languages/c/programming-bbrown/c_086.htm 

Evilrix, I don't know where the repeat comes from.  If it's me, it's one of my tutoring methods that's been successful in getting to the "Oh....I see" moment.  It doesn't work for everyone.  It works for some students.

Picasso, L-> is like (*L).  Please look at farzanj's post again.  Then look at my first post with code.  Replace line 9 with

    return (*L).next == NULL;

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Mostly L-> is easier to type and read.

sonagu's reference is very good if you need/want help understanding Linked Lists.

Evilrix, my apology if I repeated/re-worded the previous post, although I never though it was against EE policy and if it is please quote it.