I can't understand the meaning of this n &= n - 1;

uint a = 0b_1111_1000;
uint b = 0b_1001_1101;
uint c = a & b;
Console.WriteLine(Convert.ToString(c, toBase: 2));
// Output:
// 10011000

Quote:

For bool operands, the & operator computes the logical AND of its operands.
The unary & operator is the address-of operator

Quote:

The output of bitwise AND is 1 if the corresponding bits of two operands is 1. If either bit of an operand is 0, the result of corresponding bit is evaluated to 0.

12 = 00001100 (In Binary)
25 = 00011001 (In Binary)

Bit Operation of 12 and 25
  00001100
  00011001
  ========
  00001000  = 8 (In decimal)

{
    int a = 12, b = 25, c;
    c = a&b;
    Console.Writeline("Output = "+c); // prints Output = 8
}

In it, value of n=5 is getting reset to:
n = number(bit(5) & bit(4))
=> n = number((0101) & (0100))
       0101
       0100
      ======
       0100

=> n = number ( 0100 ) = 4