The Meaning of Concealment
Satr linguistically: is concealing a thing. It is the verbal noun for satara al-shay’a yasturuhu wa yastiruhu satran wa sataran (he concealed a thing, exercising concealment). Meaning, he covered it up or hid it. Whatever one conceals is mastur (concealed). That which one conceals with is its sitr (concealer, concealment).  Summarised from: al-Mufradat, al-Raghib al-Asfahani (1/396); Jamharat al-Lughah, Ibn Durayd (1/392); Tahdhib al-Lughah, al-Azhari (12/265); Magayis al-Lughah, Ibn Faris (3/132); al-Muhkam, Ibn Sidah (8/465); Mukhtar al-Sihah, al-Razi (1/142); Lisan al-`Arab, Ibn Manzur (4/343); al-Qamus al-Muhit, al-Fayruzabadi (1/404).
Satr technically: is hiding what is shameful and not protruding it. Whoever is known for uprightness but fell into sin it is concealed and he is advised.  al-Targhib wa al-Tarhib, al-Mundhari (3/237); Fath al-Bari, Ibn Hajar (5/117); Fath al-Qawiyy al-Matin, Sh. `Abd al-Muhsin al-`Abbad (p. 122). The Difference between Concealment and Forgiveness (Ghufran), and between Concealment, Veiling (Hijab), and Covering (Ghita’)  al-Furuq al-Lughaiyyah, al-`Askari (p. 288); al-Kulliyyat, al-Kafawi (1/666).
Forgiveness entails removal of punishment and gaining reward. No one deserves this except the believer, and it is not used except when referring to the Creator, exalted. Concealment is more specific than forgiveness, since it is possible to be concealed but not forgiven.
A veil is the prevention itself as well as that which prevents. Concealment is that which is used to conceal. It is possible to say: the veil of a thing is what was intended to be concealed. Another difference is that concealment does not prevent entering upon the concealed, but veiling does.Commandments of Concealment and Encouragement towards it in the Qur’an and Sunnah
❖ Allah, exalted, says: “Indeed, those who love to see indecency spread among the believers will suffer a painful punishment in this life and the Hereafter. Allah knows and you do not know.” al-Nur: 19. Meaning, those who choose that ugly speech becomes prevalent about them.  Tafsir Ibn Kathir (6/29).
❖ He, says, exalted: “Do not spy on one another.” Meaning, accept what is apparent to you and leave what Allah has concealed.
❖ Abu Hurayrah, Allah be pleased with him, said: “The Messenger of Allah ﷺ said: ‘All of my Ummah will be fine, except those who are public in committing sin. A form of such disclosure is that a person commits a sin at night and though Allah conceals it from the public, he comes in the morning and says: ‘So-and-so, I did such-and-such thing yesterday.’ He spent the night concealed by his Lord, then in the morning he removes Allah’s concealment from himself.’”  Reported by al-Bukhari (6069) and this is his wording, as well as Muslim (2990).
❖ Abu Hurayrah, Allah be pleased with him, said: “The Messenger of Allah ﷺ said: ‘He who alleviates one of the worldly sufferings of a believer, Allah will alleviate one of his sufferings in the next life. He who conceals the faults of a Muslim, Allah will conceal his faults in this world and the next. Allah is at the aid of a servant so long as the servant is at the aid of his brother.’”  Reported by Muslim (2699). Quotes of the Predecessors and Scholars on Concealment
❖ Abu Bakr al-Siddiq, Allah be pleased with him, said: “If I am to grasp a drinker, I would in fact prefer that Allah conceals him; and if I am to grasp a thief, I would have preferred that Allah conceals him.”  Reported by Ibn Sa`d in al-Tabaqat al-Kubra (5783) abridged, and Ibn Abi Shaybah in al-Musannaf (28664), and this is his wording. Ibn Hajar authenticated its chain in al-Isabah (1/575).
❖ Abu al-Sha`tha’ narrates: “Shurahbil ibn al-Simt was commanding an army. He said to them: ‘You have reached a land with many women and much drink. Whoever among you surpassed a limit, let him come to us so that we may purify him.’ This reached `Umar ibn al-Khattab who wrote to him, saying: ‘Are you the motherless one who commands people to unveil Allah’s concealment which He covered them with?!’”  Reported by `Abd al-Razzaq in al-Musannaf (9371) and Hinad in al-Zuhd (2/246).
❖ al-Hasan al-Basri said: “Whoever has some matter that is concealed between him and his brother, let him not unveil it.”  Reported by al-Khara’iti in Makarim al-Akhlaq (441). Concealment Does Not Entail Not Enjoining Right and Forbidding Wrong
Concealing another does not mean that one does not admonish them privately. If he is advised and rebuked, then does not desist from his ugly deed and then commits it publicly, it is permissible at that point to bear witness against them legally, as has been stated by our scholars. Concealment is exercised in a sin that has passed. One still admonishes the sinner for the sin they have committed as a matter of obligation. If not, he raises his matters to court. This is not a form of unlawful backbiting, rather necessary advice.  Fath al-Bari, Ibn Hajar (5/97); Hadhihi Akhlaquna, Mahmud al-Khazandar (p. 452); with adaptation. Benefits of Concealment
❖ Spreads love and sociability among the believers
❖ It aids the sinner to reprimand and reproach himself, repenting to Allah sincerely.
❖ Exposing people - especially those of virtue who slipped up - encourages the laity to sin.
❖ The soul of the one who conceals is pure and Allah is pleased with him, concealing him in this life and the next.Forms of Concealment
The Muslim concealing himself, such that he does not spread knowledge of his sins even if it be to his friends, except for legal enquiry.  Khuluq al-Mu’min, Mustafa Murad (p. 113). The Muslim concealing his Muslim brothers. Concealing the deceased. If he is performing his ritual washing and sees from him that which is shameful, he must hide it. Means to Acquiring Concealment
To know the virtue of concealment, and that whoever hides the faults of his Muslim brother, Allah covers up his faults in this world and the Hereafter. To appreciate the meaning of brotherhood. To put oneself in the place of one's brother who slipped up and sinned. Just as one would like to be concealed, so would he. To worry about rectifying one’s own affairs. Concealment in Poetry
Ahmad Shawqi said:
“Whoever does not stand up to conceal others
Lives having all attack his honour, uncovered.”  Diwan Ahmad Shawqi (p. 262).