The Meaning of Worship
Taken from the explanation of Kitāb al-Tawḥīd – the monumental work of Shaykh al-Islām Muḥammad ibn ͑ʿAbd al-Wahhāb (d.1206) – raḥimahullāhu Taʿālá – it will serve as an excellent introduction..
And ͑ ibādah is obedience to Allāh by acting upon what He commands, and abandoning what He forbids, and this is the reality and essence of Islām. And the meaning of Islām is: istislām (submission and surrender) to Allāh – the Most High – along with the utmost compliance, humility, and submissiveness to Him.
Shaykh ͑ Abd al-Raḥmān ibn Ḥasan Āl al-Shaykh
THE MEANING OF WORSHIP:
The statement of Allāh – the Most High - :
“I did not create the Jinn, nor mankind, except to worship Me” [Sūrah al-Dhāriyāt, 51:56].
Shaykh al-Islām Ibn Taymīyyah (d.728H) – raḥimahullāh – said: “Worship (al-ʿĪbādah) is obedience to Allāh by following that which He ordered upon the tongues of His messengers.” He also said, “Worship (al-ʿĪbādah) is a comprehensive term covering everything that Allāh loves and is pleased with – whether sayings or actions, outward and inward.” 
Ibn al-Qayyim (d.751H) – raḥimahullāh– said: “Worship revolves around fifteen principles. Whosoever completes them has completed the stages of ʿubūdiyyah (servitude to Allāh). The explanation of this is that ’ʿibādah is divided between the heart, the tongue, and the limbs. And that for each one of these three come five types of rulings, covering all actions: wājib (obligatory), mustahabb (recommended) ḥarām (prohibited), makrūh (disliked), and mubāh (permissible)." 
Imām al-Qurṭabī (d.671H) – raḥimahullāh– said: “The root of ʿibādah is humility and submissiveness. The various duties that have been prescribed upon the people are called ’ʿibādāt [acts of worship] since what is required is that these acts of worship must be done with humility and submissiveness to Allāh – the Most High.” 
Ibn Kathīr (d.774H) – raḥimahullāh – said: “And ʿibādah is obedience to Allāh by acting upon what He commands, and abandoning what He forbids, and this is the reality and essence of Islām. And the meaning of Islām is: istislām (submission and surrender) to Allāh – the Most High – along with the utmost compliance, humility, and submissiveness to Him.”
He also said whilst explaining the above āyah: “Indeed Allāh – the Most High – created the creation so that they could worship Him alone, without associating any partner with Him. Whoever obeys Him will be completely rewarded, whereas whoever disobeys Him would be punished with a severe punishment. And He has informed that He is neither dependant nor does He have any need for them. Rather, it is they who are in dire need of Him, in every condition and circumstance, since He is the One who created, sustains, and provides for them.” 
THE MEANING OF ṬĀGHŪT:
The statement of Allāh – the Most High - :
“And to every nation We sent messengers, ordering them that they should worship Allāh alone, obey Him, and make their worship purely for Him; and that they should avoid al-ṭāghūt” [Sūrah al-Naḥl, 16:36].
And al-ṭāghūt is from the word al-tughyān, which means: going beyond the limits.
ʿUmar Ibn al-Khaṭṭāb (raḍī Allāhu ʿanhu) said, “The ṭāghūt is Shayṭān.” 
Jābir (raḍī Allāhu ʿanhu) said: “The ṭāghūts are the soothsayers and fortune-tellers upon whom the devils descend.” 
Imām Mālik (d.179H) – raḥimahullāh– said: “Ṭāghūt: that which is worshipped besides Allāh.” 
So this is what has been mentioned by certain people. However, Imām Ibn al-Qayyim – raḥimahullāhu ta’aʿalá – has given a very comprehensive definition. He said, “The ṭāghūt is all that which causes the person to exceed the limits with regards to that which is worshipped, followed, or obeyed. So the ṭāghūt in any nation is whosoever turns to other than Allāh and His Messenger for matters of judgement or is pleased to be worshipped besides Allāh, or is followed without clear proof from Allāh or is obeyed in that which is known to be disobedience to Allāh.” 
 Fat‘h al- Majīd li-Sharḥ Kitāb al-Tawḥīd (1/84-90).
 Majmūʿ al-Fatāwá (10/149) of Ibn Taymīyyah.
 Madārij al-Sālikīn (1/109)
 Al-Jāmiʿ li-Aḥkāmil-Qurʾān (1/225), and (17/56) of al-Qurṭabī.
 Tafsīr al--Qurʾānil-ʿAdthī m (7/402)
 Related by al-Tabarī in Jāmiʿul-Bayān ’an-Ta‘weelil-Qurʾān (no. 5834), al-Ḥāfiẓ Ibn Ḥajar said in Fat′h al-Bārī (8/251), “Its chain of narrators is strong.”
 Related by al-Tabarī in his Tafsīr (no. 5845)
 Related by as-Suyootee in al-Durarul-Manthoor (2/22), by way of Ibn Abī Ḥātim.
 I’lāmul-Muwaqqi’een (1/53)