Lingam means identification, a symbol through which you can identify what the truth is, what the reality is. What is not visible but yet can be identified by one thing that is Lingam. When a baby is born, how do you know whether the baby is a male or female? Only through one part of the body can you identify whether this baby is a boy or a girl. Otherwise babies look alike until a certain age. But one part tells you what the future is. And that is the reason the genital is also called Lingam. Similarly how do you identify the Lord of this Creation? He has no form. So then they said that there should be a sign to identify Him. So the sign, by which you identify both the male and female forms, combining them both to form one single symbol to identify the Lord who has no form or identity, who is all pervading in this entire Brahmanda (Creation), is Shiva Lingam.
That is why it is said, Namamishamishana Nirvanarupam Vibhum Vyapakam Brahmavedasvarupam.
Nirvanarupam – He has no form or body; Vibhum – He is present everywhere; Brahmavedasvarupam – He is the personification of Supreme Knowledge.
See, how does internet work, how do telephones work? How do all these things work? In the space (Aaakasha), there is knowledge present in every particle. Here, right now, where we all are sitting, so many channels of the world are running, so many vibrations are present, so many e-mails are present right here. That is why when you open your computer and open your e-mail all those e-mails get downloaded into your computer.
All the characters that you type and send via SMS are present in this space! If you get angry at someone, that too stays in the space. If you congratulate someone, that too stays in the space. That is how all this gets transferred in another cell phone, and that is why in this space element (Akash tattva), knowledge is inherently present. And not just of today but knowledge even from thousands of years back is present here. This very moment you can see what had happened thousands of years back and what is going to happen in the next thousand years; you can see all that because it is all written, all recorded in the space, and it is all present right here.
So how does one recognize that space element (Aakash tattva)? The ancient people kept a round stone and through it we remember the Creator.