A POS terminal is mainly used to accept card payments at a physical point of sale, while a payment gateway enables merchants to accept and process payments online.
For a business, the practical comparison should cover where customers pay, setup and integration requirements, transaction fees, settlement timing, supported payment methods, and any recurring charges or contractual obligations.
The figures, fees and limits in this answer vary by bank and change over time — confirm them with your bank or the official source before acting.