IPO vs FPO - The Conclusion:
The difference between IPO and FPO can be summarized as follows:
IPO is the first public issue of the shares of a private company that is going public. On the other hand, FPO is the second, third or subsequent public issue of the shares of an already listed company (public company).
IPO is released with an intention to raise capital through public investment.
Should You Invest in IPOs? - Phil Town
Unlike FPO, that is offered with an aim to inflow subsequent public investment.
IPO are relatively riskier than FPO. Since in IPO, an individual investor doesn't know of what is going to happen with the company in future.
But in the case of FPO the company is already listed on stock exchange, so investors can study the past performance of the company and make an assumption about the company's future growth prospects.