There are some characters which are special and need to be escaped. Like when you define a string
str = " this is test string \
and this contains multiline data \
do you understand the backslash meaning here \
it is being used to denote the continuation of line"
In a string defined in a double quotes "", if you need to have a double quote how would you doo that? "\"", this is why when you put a backslash in a string you are telling interpretor you are going to use some special characters and which are escaped by backslash. So when you read a "\" from a file it will be read as "\" this into a ruby string.
char = "\\"
char.length # => 1
I hope this helps ;)