A QR code is a two-dimensional barcode that stores a URL, text, contact card, or Wi-Fi credentials and is read by pointing a phone camera at it.
Also called: Quick Response code · QR
QR was invented by Denso Wave in 1994 for the automotive industry. It uses a grid of black and white squares with error-correction so it still scans if part of the code is dirty or covered.
Common payloads: a link (the vast majority), a vCard for contact sharing, a Wi-Fi network for guests, a UPI or payment intent, or a plain-text message.
Higher error-correction levels let you overlay a logo or icon without breaking scanning — usually up to 30 % of the code area is safe.
HTTPS is HTTP wrapped in TLS encryption — it protects requests and responses in transit and proves to the browser that the site is who it claims to be.
Compound interest is interest calculated on the original principal plus all previously earned interest — the mechanism that makes long-term investments grow exponentially.
EMI is a fixed monthly payment — combining principal and interest — that a borrower pays a lender until a loan is fully repaid.