$data is a scalar variable, while @data is an array

   

$data = "Here's the data.";
@data = (1, 2, 3);

print $data;
print @data;

1.	Constant scalar
2.	Convert to scalar
3.	Creating a Scalar
4.	Declare scalar variable to store the integer value
5.	Naming Scalar Variables
6.	Program to illustrate the use of scalar variables.
7.	scalar value interpolation
8.	Scalars (Denoted by $)
9.	Simple calculation with scalar variable
10.	A scalar is a variable that holds a single value, a single string, or a number.
11.	A scalar variable can reference a string value or a numeric value.
12.	Assign new value to the integer scalar variable
13.	Compound assignment operator with scalar variable
14.	Concatenate two scalar variables with double quotes
15.	Initializing scalars and printing their values
16.	Perl supports integers (decimal, octal, hexadecimal), floating point numbers, scientific notation, Booleans, and null.
17.	Merge scalar variable into the string for output
18.	If there are no quotes, then Perl has to decide whether the value is a string or a numeric value.
19.	Scalar variables hold a single number or string and are preceded by a dollar sign ($).
20.	Curly Braces

$data is a scalar variable, while @data is an array : Scalar « Language Basics « Perl