Author:Shaykh ’Abdur-Rahmaan Ibn Hasan aalush-Shaykh (d.1258H)
Source:His commentary Fathul-Majeed li-Sharh Kitaabit-Tawheed (1/84-90)
THE MEANING OF WORSHIP: 
The statement of Allaah, the Most High: “I did not create the Jinn, nor mankind, except to worship Me.” [Sooratudh-Dhaariyaat 51:56]
Shaykhul-Islaam Ibn Taymiyyah (d.728H) – rahimahullaah – said:
“Worship (al-’Ibaadah) is obedience to Allaah by following that which He ordered upon the tongues of His Messengers.” He also said, “Worship (al-’Ibaadah) is a comprehensive term covering everything that Allaah loves and is pleased with – whether saying, or actions, outward and inward.” 
Ibnul-Qayyim (d.751H), rahimahullaah, said:
“Worship revolves around fifteen principles. Whosoever completes them has completed the stages of ’uboodiyyah (servitude to Allaah). The explanation of this is that ’ibaadah 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: waajib (obligatory), mustahabb (recommended), haraam (prohibited), makrooh (disliked), and mubaah (permissible).” 
Imaam al-Qurtubee (d.671H), rahimahullaah, said:
“The root of ’ibaadah is humility and submissiveness. The various duties that have been prescribed upon the people are called ’ibaadaat (acts of worship), since what is required is that these acts of worship must be done with humility and submissiveness to Allaah, the Most High.” 
Ibn Katheer (d.774H), rahimahullaah, said:
“And ’ibaadah is obedience to Allaah by acting upon what He commands, and abandoning what He forbids; and this is the reality and essence of Islaam. And the meaning of Islaam is: istislaam (submission and surrender) to Allaah, the Most High, along with the utmost compliance, humility, and submissiveness to Him.”
He also said whilst explaining the above aayah:
“Indeed Allaah, 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 TAAGHOOT:
The statement of Allaah, the Most High: “And to every nation We sent Messengers, ordering them that they should worship Allaah alone, obey Him, and make their worship purely for Him; and that they should avoid at-Taaghoot.” [Sooratun-Nahl 16:36]
And at-taaghoot is from the word at-tughyaan, which means: going beyond the limits.
’Umar Ibnul-Khattaab (radiyallaahu ’anhu) said:
“The taaghoot is Shaytaan.” 
Jaabir (radiyallaahu ’anhu) said:
“The taaghoots are the soothsayers and fortune-tellers upon whom the devils descend.” 
Imaam Maalik (d.179H), rahimahullaah, said:
“Taaghoot: that which is worshipped besides Allaah.” 
So this is what has been mentioned by certain people. However, Imaam Ibnul-Qayyim, rahimahullaahu, has given a very comprehensive definition, so he said, “The taaghoot is all that which causes the person to exceed the limits with regards to that which is worshipped, followed, or obeyed. So the taaghoot in any nation is whosoever turns to other than Allaah and His Messenger for matters of judgement; or is pleased to be worshipped besides Allaah; or is followed without a clear proof from Allaah; or is obeyed in that which is known to be disobedience to Allaah.” 
 Fathul-Majeed li-Sharh Kitaabit-Tawheed (1/84-90)
 Majmoo’ul-Fataawaa (10/149) of Ibn Taymiyyah.
 Madaarijus-Saalikeen (1/109)
 Al-Jaami’ li-Ahkaamil-Qur‘aan (1/225), and (17/56) of al-Qurtubee.
 Tafseerul-Qur‘aanil-’Adtheem (7/402)
 Related by at-Tabaree in Jaami’ul-Bayaan ’an-Ta‘weelil-Qur‘aan (no. 5834), al-Haafidh Ibn Hajar said in Fathul-Baaree (8/251), “Its chain of narrators is strong.”
 Related by at-Tabaree in his Tafseer (no. 5845)
 Related by as-Suyootee in ad-Durarul-Manthoor (2/22), by way of Ibn Abee Haatim.
 I’laamul-Muwaqqi’een (1/53)