A meme is basically an idea or concept that self-propagates. Like a virus, it spreads from host mind to host mind, mutating, changing, and passing from mind to mind via gossip and communication transference. In a way almost paralleling Darwinian selection the most successful ideas spread like a viral plague across populations, till almost everyone knows of them.
Memes less successful at propagation, die out. Thus, memetic propagation and memetic engineering are at the heart of good marketing for any project, virtual or otherwise.
Memetic engineering is a term concerned with the process of modifying held ideas and beliefs by exposing those who carry those beliefs to differing belief systems that question their existing set.
In other words, memetic engineering is basically the control, monitoring and managing of the flow and quality of information.
It is assisting memes that otherwise might die out, gain a hold in the population. At the same time, it is the suppressing, reengineering or twisting of strong memes that would otherwise survive, by mutating their perception in people?s minds so as to encourage their dissipation.
It is essentially the dream of any marketer, or government official - ultimately offering the potential for control of knowledge.
Internet based environments and the free-for-all social elements of virtual environments to a large degree counteract direct memetic engineering.
That said, a virtual environment is also to a large extent, a controlled, sealed environment with a specific population. They are thus places where memetic engineering techniques can be practiced at close to petridish levels.