There are 3 main categories in IPO:
1. Qualified Institutional Buyer or QIB (50% of offer size reserved) - Allotment is done in Proportionate way.
Commercial banks, mutual funds, FPIs are part of QIB Category.
2. Retail Individual Bidders or RII (35% of offer size reserved) - The Allotment to each Retail Individual Investor shall not be less than the minimum Bid Lot, subject to availability of Equity Shares in the Retail Portion and the remaining available Equity Shares if any, shall be allotted on a proportionate basis.
Resident Indian individuals, Eligible NRIs and HUFs are part of RII category.
The bid amount in RII category should not exceed Rs 200,000.
3. Non-Institutional Bidders or NII or HNI (15% of offer size reserved) - Allotment is done in Proportionate way.
Resident Indian individuals, Eligible NRIs, HUFs, companies, corporate bodies, scientific institutions, societies and trusts are part of NII. High Net-worth Individuals (HNI) applying for over 2 lakhs in an IPO falls in this category.
The bid amount in NII category is above Rs 20,000. As the allotment is done in proportionate basis, every applicant get some shares.
Mainly individual investor who take IPO Funding applying in NII category. This category is highly oversubscribed as the size is small and people get crores of IPO funding.
Hope this help.