IPO (Initial Public Offering) is a traditional way of buying stocks of a company. And as the term initial mean fist time in history of company they are offering some share to general public.
To go public investment bank is mendatory in IPO. But this doesn't mean this only new companies can do IPO, Many of the successful companies in later part of their time can also do IPO
if they want to raise money to expand or to invest in another plant or equipment. When people invest in IPO the become shareholder of the company.
ICO (Initial Coin Offering) is related to crypto as most of the cryptocurrencies companies do ICO when they are in their initial stage and need some funds to develop their MVP or the main idea
behind the project. And most of the crypto exchanges also do ICO as well to generate some money in initial stage. But in ICO case when you invest in ICO you don't get any shares you will get
some coins or tokens respective to the amount you invest. For example if you want to participate in ICO of Bither Platform you will invest in the ICO and you will get some tokens lets say 100000 BTR
this means you only have these coins and company is not yours.
STO (Security Coin Offering) are connected with both ICO and IPO in some ways like in ICO they offer the coins/tokens to General Public but difference is they are backed up by SEC and if they don't follow the
rules and regulations they may have to pay some fine/penalty. And they have to pass some tests like KYC etc and many more to be considered as Security. And they are related with IPO in this way that their prices
are directly link with company's profit and loss. And profit and loss can effect the prices of STOs.