Portuguese dialects are mutually intelligible variations of the Portuguese language over Portuguese-speaking countries and other areas holding some degree of cultural bond with the language. Portuguese has two standard forms of writing and numerous regional spoken variations (with often large phonological and lexical differences).
The standard written form of Portuguese used in Brazil is regulated by the Brazilian Academy of Letters and is sometimes called Brazilian Portuguese (although the term primarily means all dialects spoken in Brazil as a whole).
In Portugal, the language is regulated by the Sciences Academy of Lisbon, Class of Letters and its national dialect is called European Portuguese.
For historical reasons, the dialects of Portuguese spoken in Africa are generally closer to those of Portugal than the Brazilian dialects, but in some aspects of their phonology, especially the pronunciation of unstressed vowels, they resemble Brazilian Portuguese more than European Portuguese. They have not been studied as exhaustively as European and Brazilian Portuguese.
Asian Portuguese dialects are similar to the African ones and so are generally closer to European Portuguese.
Differences between Brazilian and European written forms of Portuguese occur in a similar way (and are often compared to) those of American and British English. There are quite a few differences in spelling. Differences in syntax and word construction, not directly related to spelling, are also observed.
The differences between the various spoken Portuguese dialects are mostly in phonology, in the frequency of usage of certain grammatical forms and especially in the distance between the formal and informal levels of speech. Lexical differences are numerous but largely confined to "peripheral" words, such as plants, animals, and other local items, with little impact in the core lexicon.
Dialectal deviations from the official grammar are relatively few. As a consequence, all Portuguese dialects are mutually intelligible although, for some of the most extremely divergent pairs, the phonological changes may make it difficult for speakers to understand rapid speech.
Here are a few examples to illustrate the differences between Brazilian and European Portuguese: