The Shielder, The Protector, The Preventer.
Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is Al-Mani (in Arabic: ٱلْمَانِعُ). There is no one to give what he's withheld or to prevent what He gives. He protects people from harmful situations and prevents undesirable actions. All is done according to His infinite wisdom and mercy.
From the root mim-nun-ayn (م ن ع) which has the following classical Arabic connotations: to prevent, hinder, hold back, restrain, deny, impeding, resist, to forbid, refuse, prohibit, to guard, defend, or to protect.
The name of Allah, al-Mani, The Protector. As we've mentioned in previous names, different scholars have different criteria for what qualifies as a name of Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ. Of the 99 names, 81 are explicitly mentioned in the Qur'an. Therefore, there is not one agreed-upon list for the remaining 18 names. Al-Mani is one of those names which is not included by certain scholars. This list includes Ibn al-Wazir, Ibn Hazm, and Ibn al-Uthaymeen, among others. However, others, such as Ibn Arabi, Imam al-Bayhaqi, and al-Ghazali, have included this name in their lists.
Al-Mani is the one who gives and the one who withholds. When He gives, there is nothing that can come in its way to prevent it. If he decides to withhold, no one can subsitute and give it instead. Similar to the names al-Hafeedh (The Protector) and Al-Qabid (The Restricting). These names are meant with a positive connotation, Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ gives and prevents with his infinite wisdom, judgement, and mercy. He is just and does not withhold because He wishes for His servant to be inflicted with pain. Instead, His witholding is defense or a shield from that which we do not know. It is a benefit that will serve you either in this life or the akhirah.
Maaa afaaa’al laahu ‘alaa Rasoolihee min ahlil quraa falillaahi wa lir Rasooli wa lizil qurbaa wal yataamaa walmasaakeeni wabnis sabeeli kai laa yakoona doolatam bainal aghniyaaa’i minkum; wa maaa aataakumur Rasoolu fakhuzoohu wa maa nahaakum ‘anhu fantahoo; wattaqul laaha innal laaha shadeedul-‘iqaab
"And what Allah restored to His Messenger from the people of the towns – it is for Allah and for the Messenger and for [his] near relatives and orphans and the [stranded] traveler – so that it will not be a perpetual distribution among the rich from among you. And whatever the Messenger has given you – take; and what he has forbidden you – refrain from. And fear Allah; indeed, Allah is severe in penalty." — (Qur'an 59:7)
Innal laaha yudaafi’ ‘anil lazeena aamanoo; innal laaha laa yuhibbu kulla khawwaanin kafoor (section 5)
"Indeed, Allah defends those who have believed. Indeed, Allah does not like everyone treacherous and ungrateful." — (Qur'an 22:38)
Narrated by Warrad: (the clerk of Al-Mughira bin Shu`ba) Once Al-Mughira dictated to me in a letter addressed to Muawiya that the Prophet (ﷺ) used to say after every compulsory prayer: 
La ilaha illa l-lahu wahdahu la sharika lahu, lahu l-mulku wa lahu l-hamdu, wa huwa 'ala kulli shay'in qadir. Allahumma la mani'a lima a'taita, wa la mu'tiya lima mana'ta, wa la yanfa'u dhal-jaddi minka l-jadd
"There is no Deity but Allah, Alone, no Partner to Him. His is the Kingdom and all praise, and Omnipotent is he. O Allah! Nobody can hold back what you gave, nobody can give what You held back, and no struggler's effort can benefit against You"
Amman haazal lazee yarzuqukum in amsaka rizqah; bal lajjoo fee ‘utuwwinw wa nufoor
"Or who is it that could provide for you if He withheld His provision? But they have persisted in insolence and aversion." — (Qur'an 67:21)
The believer benefits from knowing al-Mani. During times of difficulty, practice sabr (patience), and Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ will reward you for how well His servant responded to the adversity. There is always something you can gain from either situation.
 Sahih al-Bukhari 844