Demonstratives are words that make a noun more or less determined. English has two: this and that, while Spanish has three: ‘este’, ‘ese’ and ‘aquel’. ‘Este’ refers to something that is near the speaker (in time or space), ‘ese’ to something that is further away, and ‘aquel’ to something that is even more far away. ‘Este libro es pesado’ = ‘This book is heavy’, ‘Ese libro es pesado’ = ‘That book is heavy’, ‘Aquel libro es pesado’ = ‘That book over there is heavy’.