As what the term implies, it simply means making your penis bigger, when it is relaxed or erect.
But how does a man enlarge his penis, or is it possible in the first place? To answer this question, we must first understand the basics of the penis structural anatomy.
The penis consists of 3 main areas, 2 large ones on top (known as Corpora Cavernosa) and 1 smaller one at the bottom (known as Corpus Spongisum). These are tissues which hold blood and determine the length of your penis when erect. These spongy tissues are actually erectile tissues.
When you have an erection, there is an increased blood flow to these tissues, and the maximum length and girth of your erected penis is the maximum amount of blood the tissues can hold.
The key to natural penis enlargement is to enable these tissues (especially Corpora Cavernosa) to hold more blood when you get excited sexually. By making the Corpora Canvernosa able to hold more blood during an erection, you will have a bigger penis, in term of length and girth. And the penis will be harder and stronger during erection.
Human body has this innate ability of growing and adapting to change, just like exercising your arms with weights training will result in muscles build up. The tendons, ligaments, and cellular tissue stretch and heal to adapt to new stressors exerted on them over a period of time. The same goes for penis, by developing and expanding the spongy Corpora Cavernosa tissues, our body will adapt to the expanded tissues over a period of time and thus the tissues will be able to hold more blood, making the penis larger.
There are different methods of penis enlargement, be it natural methods (like exercises) or via surgery. Natural methods of penis enlargement methods work on the basis of expanding and developing the Corpora Cavernosa, enabling them to hold more blood when there is an increased blood flow, thus resulting in a bigger and harder penis when erect.