Smishing is a type of phishing attack that uses text messages or common messaging apps to trick victims into clicking on malicious links or providing personal information. The scenario in the question describes a smishing attack that uses pretexting, which is a form of social engineering that involves impersonating someone else to gain trust or access. The unknown number claims to be the company's CEO and asks the employee to purchase gift cards, which is a common scam tactic. Vishing is a similar type of attack that uses phone calls or voicemails, while phishing is a broader term that covers any email-based attack.