Problem Detail: I am currently reading Introduction to the Theory of Computation (Sipser), and after introducing epsilon labeled transition arrows, the book shows the following NFA: 
I was following it until I read the following :
I was following it until I read the following :
Practice with it to satisfy yourself that it accepts the strings ϵ, a, baba and baa…
What does an input string of ϵ mean?
Asked By : jcw
Answered By : collapsar
In the context of NFAs, $epsilon$ marks state transitions that do not consume input. These transitions thus express the non-determinism of the automaton. When discussing the acceptance of $epsilon$, the symbol marks the empty string (this is equivalent to the condition that an accepting state is reachable by a sequence of $epsilon$-transitions from the start state). to avoid confusion, some authors use a different symbol for the empty string (often $lambda$).
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