IPO as it suggests it is the initial public offering and the particular stake is open for the public in the capital markets and listed on the exchanges i.e NSE,BSE,etc
OFS on the other hand is a method for promoters to further dilute or offload its stake.
Note that , here the company is already listed on the stock exchange and the promotor is willing to dilute its stake . A separate window is provided for the trade under OFS.
