Hello Amit,
Suppose you passed in year 2018 and you are going to take admission In 2019. Then in this case, There is gap of 1 year. So you have to provide a certificate, Stating that where you spend this 1 year, why there is 1 years gap in your study.
Don't worry, this is not a big deal.
In case, you have passed in 2018 and going to take admission in this year itself then no need to produce gap certificate even if you give improvement results.
Good Luck.