Checkout What The Darkspot On Muslims Forehead Is Called And What It Means

Darkspot seen on a Muslim foreheads is called Zebibah and in English, it is called the prayer bump. The Darkspot appears as a result of praying.

 As a Muslim it is expected to pray atleast five times in a day. These five  prayers are mandatory, each prayer has a timeframe within which it has to be prayed. These five mandatory prayers exactly 17 rakahs and a rakah in a single unit of  a prayer. Each rakah involves kneeling twice. As such, a practicing muslims put his forehead 34 times in a day. 

When done firmly for extended period of time, dark spot develop on the forehead which may be considered as a sign of piety and dedication.

It is mostly believed that Muslims with the darkspot will have their forehead shining light and illuminated on the last day, the judgement day. This is according to an Hadith of the holy Prophet Muhammad saw.

Note that a Muslim who don't have this mark doesn't mean that person doesn't pray five times a day neither it is a sign of righteousness or a prove that you will enter heaven but it means that you pray a lot.