Visualization is one aspect of the Law of Attraction. In the simplest definition, visualization is the process when you create a visual image in your brain. It is used to help the universal mind to discover what you want.
But luckily it's not that as straightforward as something like "you think it and it will come true." Otherwise, every time we think of any random thoughts they will activate the Law of Attraction and we will materialize anything good or bad, noble or evil things we can imagine.
Another factor to consider is that we think in terms of positive and negative imagery. If it were as simple as getting whatever your thoughts show, you would get a lot of bad things as well as good. And it is true that people who focus primarily on the negative tend to have more negative aspects of their lives occur. The conclusion is it takes more than just random thoughts to make it work.
Visualization techniques help set your mind to create clear images of what you are looking for. As you continue to create those images, it is easier for them to be picked up by the Universe. While this sounds like a strange concept, it is not new. It has been around since the late 19th century although some believe even earlier than that.
If you are skeptical about this concept, think back to a time when someone who you haven't seen in a while pops into your head. You see their mental picture quite clearly. Then, a short time later, you receive a communication from them, either in the form of an email or a call. Often, they have some unexpected news to tell you.
The question you have to ask is, did you come up with the image of that person or did they do so and transmit their need to contact you? It's likely you have already had similar experience several times in your life. If you haven't, there are plenty of others who can attest to it and may even be able to tell you the people it happened with.
Something else that happens to people is when someone they know well dies.
They seem to know the moment it is happening. They visualize the person in their head and know something is not right and then when they find out the person died, they make the connection. It is an odd sensation, but it gives some thoughts again on the Law of Attraction, visualization, and the idea that everything is energy and we are all connected in some shapes or forms.