Website Promotion is a general term. It is so general, in fact, that most communications that are not strictly advertising (paid and non-personal) are characterized as promotions. But this distinction is blurry at times, so looking for a clear definition is useless. It’s better to just recognize that there are many types of promotions.
Some promotions -- special events, sampling, rebates, and coupons, to name a few -- are aimed directly at consumers. The use of these promotions can typically be tied to the hierarchy of communication effects model.
Website Advertising is generally targeted at end consumer (as opposed to the channels of distribution). It can be used for many purposes, including establishing awareness, providing information for knowledge, and creating brand loyalty. In its knowledge role, advertising can communicate a positioning (or modify a positioning) and even promote new uses of a product (think "Orange Juice isn’t just for breakfast anymore").
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