Q: What is plea of alibi in murder case ?

Ans: An alibi is a defence under section 11 of evidence act and is used when a person is not present at a particular place at the time of the offence. 

Alibi means some where else or else where. 

If A claims that he was not in Delhi at the time of the offence and was instead in Chennai, he will be able to use the defence from plea of alibi .The court will make it relevant when A proves his presence in Chennai.