Specific: It is the "what, the why and the how", precise objective no ambiguity possible.
Measurable: quantified so that progress can be measured and the result evaluated.
Achievable: the bar must be set at the right level, neither too high (frustration) nor too low (boredom).
Realistic: the objective must take into account the context and external constraints.
Time-bound: a deadline is needed, either a single end date or a period (day, week, month etc.).