At a practical level, actual things and happenings as opposed to more theoretical or mathematical abstractions. However, what is 'real' in statistics has a variety of philosophical meanings, from concrete events to more idealised notions such as the 'typical user' of a system.
Also used in hcistats2e: Chap. 1: pages 3, 4, 5, 6, 9; Chap. 3: page 30; Chap. 5: pages 61, 62, 63; Chap. 7: page 76; Chap. 9: page 104; Chap. 13: page 162