Geralmente nada! Mas nela maioria de casos "perhaps" é mais formal. Aqui estejam mais detalhes de Longman Dictionary of Contemporary English: per‧haps / pəhæps, præps $ pər-, præps / adverb 1 used to say that something may be true, but you are not sure SYN maybe : Perhaps she’s next door. Perhaps it will snow tomorrow. It won’t take so long next time, perhaps. ‘I don’t think you understand.’ ‘Well, perhaps not .’ Register In everyday English, people usually use may or might rather than use perhaps it/she/they etc will : It might snow tomorrow. 2 used to give your opinion, when you do not want to be too definite SYN maybe : This is perhaps her finest novel yet. The industrial revolution was, perhaps, the most important event in history. 3 used to say that a number is only a guess SYN maybe : The room was large, perhaps 20 feet square. Perhaps 200 people were there. 4 spoken used to politely ask or suggest something, or say what you are going to do SYN maybe : I thought perhaps we’d have lunch in the garden.

they are synonyms perhaps= maybe= possibly

They basically mean the same in English too. "Maybe" is a bit more common for personal use. Maybe I'll go. Maybe I'll see you tomorrow. "Perhaps" would still be correct in these sentences. There is a common phrase - "maybe. maybe not" which means you don't know or haven't decided on something. "perhaps, perhaps not" is not a phrase which we use.