Tailgating is a security breach technique where an unauthorized person gains access to a restricted area by closely following an authorized user, typically without the user's knowledge. Since the question describes a situation where an individual enters the secure area immediately after an authorized user, without providing separate credentials, this depicts a classic case of tailgating. The other answers provided, such as 'Phishing', 'Rogue AP', and 'MAC Spoofing', describe different security threats that do not match the scenario of gaining unauthorized physical access by following behind an authorized individual.