An expression meaning there is no option but to do something; 'have no choice but to...'. Often used as '〜するほかない'.
事故で電車が止まったから、歩いて帰るほかない。
The train stopped due to an accident, so we have no choice but to walk home.
証拠がそろっていないので、いまは待つほかない。
Since the evidence isn't complete, we have no choice but to wait for now.
頼める人がいないから、自分でやるほかない。
There's nobody to ask, so I have no choice but to do it myself.