This is a very popular phrase in Spain and Latin America, also spelled as a single word (oséa or osea). The expression is generally used to introduce a rephrasing of something that you have already said. If you think of it, the meaning is quite literal: The phrase is formed out of the disjunctive conjunction o ("or") and the word sea ("would be"), the third person present subjunctive form of the verb ser ("to be"). Let's see some examples.
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O sea, vienen muchas personas de todas partes del mundo.
I mean, many people come from all over the world.
Caption 7, Cabarete - Charlie el taxistaPlay Caption
Sometimes the word que ("that") is added after o sea, without altering the meaning:
Y yo nací en un cuartel, o sea que...
And I was born in a barrack, in other words...
Caption 37, 75 minutos - Del campo a la mesa - Part 12Play Caption
Be careful: the combination "o + sea" can sometimes have a totally different meaning, so always be observant of the context:
... sea bueno o sea malo.
... whether it's good or whether it's bad.
Caption 34, Club de las ideas - Intuición - Part 1Play Caption
An additional use of the phrase o sea is also very popular in Latin America among fresas (pejorative slang used to describe stereotypically superficial upper or middle-class youngsters). In this case, o sea is used as a sarcastic remark that can be translated as "obviously," "duh," "come on," "give me a break," or "I mean," depending of the context. Our Venezuelan teen show NPS uses the expression a lot:
¡Ay pues, obvio que va a querer! ¡Porque nadie le dice que no a una chica popular, o sea!
Oh well, [it's] obvious that he is going to want to! Because no one says no to a popular girl, duh!
Captions 21-22, NPS No puede ser - 1 - El concurso - Part 10Play Caption
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