What is istighfar? What is its importance in Islam?

What does istighfar mean? What are the virtues of istighfar?

Istighfar is an Arabic word meaning; seeking forgiveness of Allah, repenting (turning back from the mistakes regretfully), praying and begging.

Mumin makes mistake, but right after He does make tawbah.

 “Mumin makes mistake, but after He does make tawba. Happy is the man who dies before he breaks his promise.” (Targib and Tarhib)

Istighfar should be made every day

 “He who does not make istighfar twice a day, he tortures himself.” (Abu Dawood)

Sins decrease with istighfar 

“If the minor sins are insisted, they don’t stay minor. If istighfar is made in the major sins, they don’t stay major.” (Dailami)