AntiChristian:
Assalamu alaikum to all my Muslim brothers and sisters!

Waleykum salaam warahmatullah wabaratuh

When we greet our fellow muslim we say-

السَّلَامُ عَلَيْكُمْ وَرَحْمَةُ ٱللَّهِ وَبَرَكاتُهُ‎

Meaning of salam?
Salam means to be cleared or delivered from defects and shortcomings. As-Salaam is also
(an attribute or) a name of Allah, the Exalted, meaning: the being who is free of all defect,
harm, change and destruction – and also safe from them.

حَدَّثَنَا شِهَابٌ، قَالَ‏:‏ حَدَّثَنَا حَمَّادُ بْنُ سَلَمَةَ، عَنْ حُمَيْدٍ، عَنْ أَنَسٍ قَالَ‏:‏ قَالَ رَسُولُ اللهِ صلى الله عليه وسلم‏:‏ إِنَّ السَّلامَ اسْمٌ مِنْ أَسْمَاءِ اللهِ تَعَالَى، وَضَعَهُ اللَّهُ فِي الأَرْضِ، فَأَفْشُوا السَّلامَ بَيْنَكُمْ‏.‏

Anas reported that the Messenger of Allah, may Allah bless him and grant him peace, said, “As-Salam (peace) is one of the Names of Allah Almighty which Allah has placed in the earth. Therefore give the greeting among yourselves.”(Al-Adab Al-Mufrad 989)

Most of the ulama (Scholars) hold that the words mean; ‘peace of Allah be on you.’ ‘you are
safe from me,’ and ‘keep me safe from you.’ In this sense, salaam will deemed to be derived
from( سلم) Salama to mean ‘well-being,’ ‘reconciliation.’ The expression would imply; ‘be
safe and secure from me and keep me to safe and secure.’

The Origin of Salam and the Reply of salam that was taught by Angels to Adam (AS):

Abu Hurairah (May Allah be pleased with him) reported:The Prophet (ﷺ) said, “When Allah created Adam (ﷺ), He said to him: ‘Go and greet that company of angels who are sitting there – and then listen to what they are going to say in reply to your greetings because that will be your greeting and your off-spring’s.’ Adam (ﷺ) said to the angels: ‘As-Salamu ‘Alaikum (May peace be upon you).’ They replied: ‘As-Salamu ‘Alaikum wa Rahmatullah (May peace be upon you and the Mercy of Allah).’ Thus adding in reply to him: ‘wa Rahmatullah (and the Mercy of Allah)’ to his greeting.” (Bukhari and Muslim)- Riyad as-Salihin 845

وعن أبي هريرة رضي الله عنه عن النبي صلى الله عليه وسلم قال‏:‏ لما خلق الله تعالى آدم عليه السلام قال‏:‏ اذهب فسلم على أولئك -نفر من الملائكة جلوس- فاستمع ما يحيونك، فإنه تحيتك وتحية ذريتك‏.‏ فقال‏:‏ السلام عليكم فقالوا‏:‏ السلام عليك ورحمة الله، فزادوه‏:‏ ورحمة الله‏”‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏‏.‏

Source: https://islamhashtag.com/