Nouns and verbs form the root س ل م

وَعَلَيْكُمُ السَّلاَمُ وَرَحْمَةُ اللَّهِ وَبَرَكَاتُهُ

 If only the word "  س ل م" or "سلم" or "سلام" (Nakirah = greeting word without beginning with ا ل), the meaning of the word is still general, ie only "safe / prosperous", (congratulations from who?)

This will be different with the word "س ل م" which is added with the prefix "ا ل" then the form of the word will be  اَلسَّلَامُ (Ma’rifat = refers to who gives "salam", that is Allah), so the meaning is "Salvation from Allah"

According to the hadith narrated by Abu Dawud and at-Tirmizi it is said that the word Salam has three types of forms, namely:

1. Short: اَلسَّلَامُ عَلَيْكُمْ

(may Allah give you salvation).

2. Medium: اَلسَّلَامُ عَلَيْكُمْ وَرَحْمَةُ اللَّهِ

(may Allah give His salvation and mercy to you).

3. Length: اَلسَّلَامُ عَلَيْكُمْ وَرَحْمَةُ اللَّهِ وَبَرَكَاتُهُ

(may Allah give His salvation and mercy, and His blessings to you).

In the Qur'an there are about 146 words "Salam" in both the form of the verb and the nouns in several surah and verses. For example: "salamun 'alaikum (Quran 6:54)," fa sallimu "(Quran 24:61)," wa assalamu (Quran 20:47). That are all have different meaning, and many more.

Hopefully useful, I apologize if I'm not good at explaining it.

Jazakallahu Khair.