Shalom (שלום) is a Hebraic word which means "peace". Like in English, it can mean the peace between two parts, as well as an inner peace, being calm or the quietness of a person. It is also used as a method of greeting like "hello", "good day (morning, afternoon, high noon,...)" or "good bye".
The root of the word "shalom" can be related to le-shalem which means "to complete, to reward, to pay, to compensate". This means that it is more than the absence of conflict or struggle or the breaking of unfriendliness: It also means a return to the balance, to justice, and to the complete equality.
In general, one uses the word "shalom" as the short form of the sentence "Shalom Aleichem" (exactly "Peace is with you") that can be translated as "good day (morning, afternoon, high noon,...)" (a greeting). This is very similar to the Arabic phrase "Salam Alaykum" (سلام عليكم) which is again a greeting meaning "Peace be with you".