Today, Google announced that it will be ending support for the Android Market app on devices with an Android version of 2.1 or earlier. On newer devices, Android Market has evolved into the Google Play Store.
It's worth noting that the company has already ended support for newer versions of the OS, including 2.3.x Gingerbread and 3.x Honeycomb, but devices running those versions can still download apps from the Play Store; it's just that Play Services isn't updated anymore.
The change is slated to happen at the end of the month, on June 30. Because of "technical restrictions in the original Android Market app", users will not receive any notification that this is about to happen.
Fortunately, this is something that will affect a very small portion of users. Android 2.1 Eclair is now over seven years old, and it's usage share doesn't even show up on Google's monthly breakdowns, meaning that it's had less than a 0.1% for years now. Naturally, this does affect even older versions as well, including Cupcake and Donut.