API

A defined interface that lets software components talk to each other; a common attack surface.

An API is a defined contract that lets software components exchange data and invoke functions, forming the backbone of web, mobile, and cloud integrations. Because APIs expose application logic directly, they are a major attack surface vulnerable to broken authentication, excessive data exposure, injection, and missing rate limiting. Defenses include strong authentication with tokens, input validation, and throttling to blunt abuse. On the exam, link API security to secure coding practices and to threats like API key leakage that grant attackers programmatic access.