What does (number & -number) mean in bit programming?

For example:

int get(int i) {
    int res = 0;
    while (i) {
        res = (res + tree[i]) % MOD;
        i -= ( (i) & (-i) );
    }
    return res;
}

A tree update function:

void update(int i, int val) {
    while (i <= m) {
        tree[i] = (tree[i] + val) % MOD;
        i += ( (i) & (-i) );
    }
}

Can you please explain what they do in the code by using ( (i) & (-i) )?