Answer:
Commoditization of a market means that the goods or services offered will be homogeneous. This means that they will be practically identical and customers will be indifferent when choosing one product or any other product because they are identical or very similar. E.g. think about gold, which is one of the most important commodities in the world. A consumer doesn't care if they are buying gold from Alaska, Canada, Brazil, etc., they are simply buying gold.
On the other hand, differentiation means that the products or services offered are heterogeneous or different. When products are differentiated, customers will buy them because they like them more than the competition. E.g. you buy Coke because you like it more than Pepsi or any other brand.
Some products will naturally tend to be commodities, e.g. agricultural products, but others go through a commoditization process that is not natural. E.g. banks offering homogeneous checking or savings account. The problem with commoditization happens when one company simply decides to offer something different. Before Amazon, internet retail was basically non-existent. But when Amazon came by, they decimated or virtually eliminated the major brick and mortar players. During many years Sears was the number 1 retailer in the world, then came Walmart. But after Amazon came, even Walmart's long term survival is doubtful and Sears, JC Penny, Toys R Us, Radio Shack, and many others are either extinct or about to become extinct. The new norm is online retailing now.