Base stats
Base stats are the general outline of statistics for a specific Pokémon species.
Base stats usually give a general idea of the strengths and weaknesses a specific Pokémon will have. For example, Umbreon is mainly a defensive Pokémon; therefore its base stats in Special Attack and Attack are low compared to their corresponding defensive stats.
Base stats range from 1 to 255, and are most often the prime representation a Pokémon species has in battle. For example, one thing many note about Chansey and Blissey are that their HP base stat is especially high; this, of course, is due to their base stats for HP being 250 and 255, respectively. However, due to this, both the Attack and Defense base stats are pitifully low for the two (both being 5 for Chansey and 10 for Blissey).
Commonly, related Pokémon will have similar base stats, though distributed differently. This is one main difference between the two or more branches of a split evolutionary line. For example, while Gardevoir's base stats for Attack and Special Attack are 65 and 125, respectively, its counterpart Gallade's Attack and Special Attack stats have inverted values.
The Pokémon with the highest total base stats are often banned from tournaments. This is because those who have the highest stats are always legendary Pokémon, with few exceptions (such as Slaking, whose base stat average is on par with Groudon and Kyogre). Pokémon of a higher evolutionary stage will also usually have higher base stats than those of a lower one, and always will have higher total stats than those of their pre-evolved counterparts (with the exception of Shedinja, whose total stats are lower than its pre-evolved form Nincada by 30).
For a list of all Pokémon by their base stats, see List of Pokémon by base stats.