Hey! Former merchant of women's apparel here.

Actually it's a bit of a mix between the two, and ecommerce is changing how that relationship works.

In a traditional buying environment, a buyer works with a portfolio of vendors, the vendors offer x amount of goods at a cost, usually massive orders. The buyer is banking on trends that they are seeing or trends they believe the customer will want, months in advance. The reaction time to the market depends on the medium (why I mentioned ecommerce)

With B&M, you've got to buy enough in advance, to where your vendor can send the product to the DC, who in turn distributes to stores. So, if I worked for say a Nordstrom, I'd be making deals right now for fall/winter.

It's entierly possible to be stuck with 9000 units of a product that nobody is fucking buying. So, when you strike gold and a product or style is flying out the door, you and marketing push like a motherfucker to squeeze every last cent out of the trend.