Linga means gender. Streelinga means feminine gender and Pulinga means masculine gender. Gender means that by which you identify that which is not yet fully expressed. This is literal meaning of Lingam.
So Shiva Linga means the Divinity is not yet expressed. It is the Divine that is inexpressible actually; beyond expression; identifying that which is not yet expressed. Knowing something which is beyond with a symbol, that is what it is.
This ancient language is so powerful. Just keep a stone anywhere and it becomes a Lingam, which means, through the stone I am thinking of something which is not yet expressed.