what does inventory means ?

Inventory, in a business sense, means items you have available to use or sell.

For instance
Sometimes a business will have a product that hasn't been selling very well, and they will put it on sale to get rid of it so they will have room for more popular items.

Or you might see a shirt you like, but not in your size, so you would ask the clerk if they have any more back in their inventory, or if they just have what you can see on the sales floor.

"Inventory" is just the word that describes a collection of goods to be sold or personal property.

Inventory can mean "an assortment of goods".

"Taking inventory" means listing and counting those goods.

When you give someone an inventory, you give them a list of those goods they've bought.