Mutual Intelligibility is a situation in which two or more speakers of a language (or of closely related languages) can understand each other. Mutual intelligibility is a continuum (that is, a gradient concept), marked by degrees of intelligibility, not by sharp divisions.
In short, when two people speak to each other in their own mother tongue to each other, and if both these languages are mutually intelligible, then both of them can very well converse each other in this manner.
Example
> Hindi and Urudu – Both are Indo – Aryan Language written in two different scripts, viz, Devanagri and Abjad Script derived from Modern Persian script, which itself is derived from Arabic Script respectively. Although only about 7% of Pakistanis speak Urudu as their first language, it is adopted as lingua franca of Pakistan. Hindi is the official language of India along with English.
>Finnish and Estonian – Finland and Estonia are situated a mere 80 km apart from each other across the Gulf of Finland. The languages of these two countries, Finnish and Estonian, were the same language (Late Proto Finnic) around 2000 years ago, but have grown apart since then.
>Tunisian Arabic and Maltese Maltese is the national language of Malta and the only Semitic official language of the European Union. Another notable point here is both nations today don’t share much of cultural similarities now though there was a history of cultural intermix in past. Today Majority of Maltese people follow Catholic Christian belief where as almost 99% of Tunisian population follow Islam.