The word 'Abd' means the subdued or subjugated. This meaning encompasses all the types of creation, higher and lower, rational and reasonless, animate and inanimate, dynamic and static, apparent and hidden, believing and disbelieving, and pious and sinning etc.. All of them are the creation of Allaah, the Mighty and Majestic. They are subjected to Him, controlled and managed by Him alone. All of them have a limit and destination and each one runs (its course) for an appointed term and does not exceed that term by an atoms worth,
“Such is the judgment of the Mighty, the all-Knowing” (YaaSeen: 38)
And if the intended sense is the worshipper, the one who loves Allaah, the one who is humble, then it refers only to the believing men and women who are Allaah's honourable slaves and those who are close to Him, who fear Him and have piety, they the ones who shall not fear, nor shall they grieve.