ASBA refers to Applications Supported by Blocked Amount. It is process created by SEBI for applying to IPOs, FPS, Rights Issues, etc. In the ASBA system, an IPO applicant’s bank account isn’t debited till the shares are assigned to them. 

ASBA as an application also comprises an approval to block the application money in the bank account while subscribing to an issue. If an investor is applying via ASBA, then their application money will be debited only if their application is chosen for allotment after the basis for it settled, or the issue is failed/withdrawn. 

Investors can submit their applications through Self Certified Syndicate Banks (SCSBs). You can check out these SCSBs on the SEBI website. There are currently around 60 such banks.