What is this technique called?

Question

public static List<Holiday> holidays {
        get {
            if(holidays == null)
                holidays=[Select h.StartTimeInMinutes, h.Name, h.ActivityDate From Holiday h];
            return holidays;
        }
        private set;
    }

Reference links if possible.

Answer 1

It's called Lazy Loading or Lazy initialization

Lazy loading is a design pattern to defer initialization until the point at which it is needed.

Reference

• Lazy Loading
• Lazy initialization

Answer 2

Well its combination of few, As Robs mentioned its caled lazy loading. Also Its called as Singleton Pattern.

Singleton pattern makes sure, you have a single instance of a particular instancein the whole transaction(in your case holidays).

Src: https://developer.salesforce.com/page/Apex_Design_Patterns_-_Singleton