A lot of people tend to make a barcode seem more complicated than it actually is. I've always considered that a barcode is a string of characters that are machine readable.

The most common barcodes, and the type that we all see when we do our shopping (remind me to tell you about my retail therapy course some time ;-) ) is known technically as linear or 1D codes typically representing upto 20 characters per code. Whilst there is no reason why a linear barcode should not encode more characters than this, I am told by my technical colleagues at Datalinx, that more than this and the size of the printable code starts to becomes too big or the thinness of the lines within the code becomes too small.

So I like to think that in very simplistic terms that the linear barcode is just like any other font, but it is special because only machines can read them. For example you get:

Now to take this a bit further:
If you 'Wiki' the word barcode, then you will be told that it is an 'optical machine-readable representation of data, which shows certain data on certain product. Originally they were represented in a linear format, such as the Code 39 above, with lines and spacings between these parallel lines.

The big advantage of 2D barcodes is that it gets over one of the restrictions of a Linear Barcode in that you can encode a lot of data into a small space, up to 2000 characters can be squeezed into a 2D code which can be a few 10’s of mm square, can you imagine how long a 1D code would be to achieve that !!

There are many common symbologies that have been adopted (and continue to be adopted) by specific industries. However, some of the common 'linear' barcode symologies that you will see in use today are: