A submission of no case to answer is an argument made by the defence, at the end of the prosecution’s case. In a criminal trial the burden is on the prosecution to prove that an offence took place, not on the defendant to prove that it did not.
No case to answer is when the defence argues that the prosecution evidence is insufficient for any reasonable court to properly convict. This means the prosecution has not produced any evidence that could be relied on to convict the defendant or the evidence is too weak. If the judge decides there is no case to answer then the case will end. If the judge rejects the submission and decides that there is a strong enough case against the defendant, it will be the defendant’s turn to call evidence.
There are other (unusual) circumstances where a case may end at this point in a trial. This includes situations where the defendant was charged with the wrong offence.