It can be understand through the following sentences:- I will not take an exam dates until i am not ready for it. (Until is use in some conditional phrase) Guest will stay here till end of this week. ( Till : can be use in timelines)

There is no difference in meaning. "until" is the regular word and "till" is an informal slang version. "Until" should always be written in formal texts though.

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Till isn't just slang it is often found in high level poetry and literature. Until would be typical in business English and non literary formal contexts.