the \ (backslash) has a number of uses, only some of which will be described here; one major use is when quoting the $, ` and " characters; in this context, the character which follows the \ is taken literally; this means, for example, instead of the back quote (`) causing command substitution, the \` is simply the back quote character (`); a "tech savvy" way to say this is that the ` "escapes" its normal function due to the backslash, and constructs using the \ are referred to as "backslash escapes"
a simple example of this can be shown using the echo command again
$ echo "Today is ` date `"
Today is Thu May 16 19:47:27 EDT 2013
$ echo "Today is \` date \`"
Today is ` date `
this is a rather trivial example that could have been produced using single quotes and no backslashes, but there will be circumstances where you want to output or use a $, ` or "; in those cases, you can substitute \$, \` and \" for the single character you really want
for example, if you wanted to output a line that says A line with command substitution contains a phrase like `date`
and simply echoed the phrase using
$ echo "A line with command substitution contains a phrase like `date`"
$ echo A line with command substitution contains a phrase like `date`
the output would be
A line with command substitution contains a phrase like Thu May 16 19:47:27 EDT 2013
instead, you need to tell the echo command that you want the ` to really be a `
$ echo "A line with command substitution contains a phrase like \`date\`"
another use of the \ is for formatting output, where character pairs such as \t have special meanings (the "tab" symbol, in this case); for example, if you want to format something using tabs (\t) and new lines (\n), you could use the following single line echo command
$ echo -e "Output\n\n\tGroup\tUsers \tTime\n\n\t1\t6\t1:45\n\t2 \t3\t6:30\n\nTotal:\t9\t8:15\n"
to produce an output that organizes the data into a table with rows and columns
note that the -e option to echo tells it to expect (and interpret properly) the character pairs starting with a \ (another set of "backslash escapes"); remember that for these backslash escapes to work, the entire line needs to be enclosed within double or single quotes