Although these terms are often used interchangeable, seeds and maps represent something different in Minecraft Pocket Edition.
What are Seeds
Seeds, or World Generation Seeds, are a user-supplied string or random number that is passed to the world generation algorithm. The world generation algorithm is responsible for defining the initial characteristics of a Minecraft PE game, including biomes, elements that exist in those biomes (like ore, plants, rivers, for example) as well as their specific location.
Seeds are either entered by a player when they start a game, or, when not provided, a random number is used.
Seeds can be shared, and, when entered on any version of Minecraft PE that is using a compatible world generation algorithm, the same initial world will render. What will not render is any changes made to the world performed by a player. We share and classify Minecraft PE Seeds (by what features are in the seed at spawn as well as by what version of Pocket Edition the seed will work on) on this site.
What are Maps
In contrast to seeds, Maps carry across both the world and any modifications that have been made by a player. For example, if a player created a Redstone calculator, or a city in MCPE, and then shared the map file with others, people using that map would see the world and the player creations in the state they were in when the map was saved. Examples of Minecraft PE Maps that can be downloaded an played are available on this site.
While seeds are entered when starting a Minecraft PE game, Maps must be installed. In Minecraft Pocket Edition, this is done through the use of third party programs as Maps are not an officially supported feature as of the time of writing this answer (0.15.4).
Just to be sure there isn’t any confusion, Maps are also a game element in Minecraft PE. In this context, maps are something a user can create which provides an overview of the areas in the game they have visited.
Last Updated Nov 15, 2016