It means a string literal, or a string raw, without considering escape characters.

The \ character acts as escape to insert special characters in string , and because it is a network address, you really want this character to be considered.

If you do not use @ , you would have to duplicate the backslash in this way:

string a = "\\servidor01\arquivos"

Here are some other examples of the content that the variable will display.

string a = "hello, world";                // hello, world
string b = @"hello, world";               // hello, world
string c = "hello \t world";              // hello     world
string d = @"hello \t world";             // hello \t world
string e = "Joe said \"Hello\" to me";    // Joe said "Hello" to me
string f = @"Joe said ""Hello"" to me";   // Joe said "Hello" to me
string g = "\\server\share\file.txt"; // \server\share\file.txt
string h = @"\server\share\file.txt";    // \server\share\file.txt
string i = "one\r\ntwo\r\nthree";
string j = @"one
two
three";

Reference: Microsoft Docs

I have two add-ons on the subject.

Reserved Word

The @ can be used for something else in the language. When you need to use an identifier that conflicts with a reserved word, this symbol can be used to indicate that it is an identifier and to resolve the ambiguity. Example:

var @lock = true;

This may be necessary for legacy codes and especially when you use a library written in another language where that word is not reserved.

New way to escape a string

In C # 6 there is a new symbol to indicate a special condition of that string . With the addition of string interpolation, we can use the variable (and maybe an expression) within string . For this the compiler needs to understand that this is being used on it. It would look like this:

var texto = $"Contei {x} vezes";

To better understand the representation of strings in C #, I suggest reading the articles:

String (C # Reference) and String literals

Briefly, C # supports two types of string representation:

Examples:

string a = "Hello";           // string regular
string b = @"Hello";          // string textual
string c = "Hello \n World";  // string regular com o escape \n de quebra de linha
string d = @"Hello \n World"; // string textual não processa combinação escape

// strings textuais podem expandir por múltiplas linhas
string e = @"SELECT * 
FROM Funcionario 
WHERE nome LIKE '%Silva%'"; 

It is a reserved language word, to escape string.

   string arquivo = @"c:\arquivo.txt";