Growth hacking is experiment-driven marketing. It's really about science. It's about process. Whereas traditional marketing promotes the products using main stream media channels in a belief that exposure brings more customers, growth hacking involves trying out different kind of tactics to expand the user base and finding out which channels and which methods outside of traditional marketing route work the best for which product or service that the startup is offering.
One of the main factor that differentiates growth hacking from the marketing is their objective. Growth hacking is a means for accelerated growth, but not the means for continuous growth and improvement.
If the conventional marketing puts the focus on the general marketing strategy for the whole company, growth hacking puts the focus on the growth. Putting out the product to the right people, obtaining the user base and finding the right channels to communicate to the people is the key for growth.
The reason why growth hacking is not straightforward to many audiences is that it does not have one set guideline that works universally for all types of startups. Growth hacking must be done using creative minds in a scientific process that is scalable, measurable and repeatable.
The "hack" is to look for creative tricks that the startup can uniquely employ. Therefore, the methods for growth hacking differs depending on the target audience and the product itself.