Interpertation $X_{\tau}$

Question

Let's say $X_i$ iid with $P(X_i=1)=P(X_i=-1)$ and $S_n=\sum_{i=0}^nX_i$. We also define the stopping time $\tau= \inf\{k:X_k=1 \}$.

How do you interpret the random variable $X_\tau$?