A map is a flat drawing of part of the Earth.
In its simplest form, minimum advertised pricing (MAP) is the lowest price a retailer can advertise the product for sale. To clarify, this does not refer to the lowest price they can sell it for in their store—just the lowest that they can show online or in an advertisement.
For example, Bose may have a MAP price of $999 for one of their speaker systems. If you put it in an ad, you may not show a price for sale lower than $999. It doesn't matter if that ad is online or in print, the rules are the same.
Before you ask, yes, this is perfectly legal under U.S. antitrust statutes. Since minimum advertised pricing only relates to “advertised” pricing and does not tell a retailer what they can sell it for in their store, this practice is legal and serves as a protection for the manufacturers. If customers begin to see they can buy your product for $699 versus the $999 MSRP, they quickly surmise that the MSRP is inflated or too high. And when that happens, no one will ever pay $999 again. Thus, making the value of your product (as a manufacturer) much less which then leads to brand erosion.
Essentially, you are limited when advertising MAP-protected products, but you can sell these products at any price you choose. This means that when the customer comes in your store, you can sell them that Bose speaker system for less than $999, if you desire.