All of us have heard of the word "puran". There are many purans for different size. The largest purana Skanda Purana is over 85000 verses long and the smallest Purana is Markandeya Purana with around 9000 verses. There are 18 Maha-Puranas or the major Puranas but there are hundreds smaller and lesser known Puranas. This includes Jain Puranas, Sthal-Puranas (Puran of a location).
The word Purana means ancient or old. All known Puranas put together are around 12 million words compared to the 3 million words of entire Mahabharata.
Puranas are often misunderstood as stories. This is because a lot of famous stories we know today have their roots in Puranas however Puranas are more like encyclopedia of our world. They have lengthy description of geography, society, cooking recipes, dates, astronomical data, geneology of kings, laws and rules of the king, moral principles, medicinal information and so on.
Agni purana for example is the primary text of vastu shastra, grammar and geography. Gaurda purana is about health and medicine and all out death related rituals come from this Purana.
Matsya Purana is what gives us all the modern puja rituals we do in temples today.
Markandeya purana gives us geography of Maharastra and Gujarat.
Vayu Purana is the oldest Purana which gives us detailed geography of Telagnada and Andhra Pradesh along with geneology of various kings.
Indian dance, music and other art forms too are inspired by Puranas. Various poses of Bharat natyam come from Bhagvadpuran.
When you look at Puranas you realizes that these are not harry potter styled fictional stories of entertainment but it is a living and breathing corpus of texts that keep us tied to our ancestors, it gives a frame of reference for our existence and culture and in some way serves the exact same purpose that modern day archeology and history try to do at some level.